Online Etymology Dictionary

hellfire (n.): also hell fire, from Old English hellefyr, in which helle is the genitive case of hell. It translates Greek gehenna tou pyros, literally "fiery hell." Also used in Middle English for "erysipelas" (mid-15c.).
hellhole (n.): "the pit of Hell," late 14c., from hell + hole (n.). Meaning "unpleasant place" is from 1866.
hellhound (n.): also hell-hound, "wicked person;" also "Cerberus," Old English hellehund; see hell + hound.
hellion (n.): 1846, American English, altered (by association with Hell) from Scottish/northern England dialectal hallion "worthless fellow, scamp" (1786), of unknown origin.
hellish (adj.): 1520s, from hell + -ish. Related: Hellishly; hellishness. Earlier in same sense were helli "helly" (late 12c.); hellen "hellish, infernal" (c.1200), with -en (2); and Old English hellic.
hello: 1883, alteration of hallo, itself an alteration of holla, hollo, a shout to attract attention, which seems to go back to at least c.1400. Perhaps from holla! "stop, cease." OED cites Old High German hala, hola, emphatic imperative of halon, holon "to fetch," "used especially in hailing a ferryman." Fowler lists halloo, hallo, halloa, halloo, hello, hillo, hilloa, holla, holler, hollo, holloa, hollow, hullo, and writes, "The multiplicity of forms is bewildering ...." Popularity as a greeting coincides with use of the telephone, where it won out over Alexander Graham Bell's suggestion, ahoy. Central telephone exchange operators were known as hello-girls (1889).
Hello, formerly an Americanism, is now nearly as common as hullo in Britain (Say who you are; do not just say 'hello' is the warning given in our telephone directories) and the Englishman cannot be expected to give up the right to say hello if he likes it better than his native hullo. [H.W. Fowler, "A Dictionary of Modern English Usage," 1926]
helluva (adj.): 1910, attempt to represent the casual pronunciation of expression hell of a _____, which is attested from 1776 (see hell).
helm (n.1): "handle of a tiller," late 13c., from Old English helma "rudder; position of guidance, control," from Proto-Germanic *halbma- (cf. Old Norse hjalm, Old High German helmo, German Helm "handle"), from PIE *kelp- "to hold, grasp" (see helve).
helm (n.2): "a helmet," c.1200, from Old English helm "protection, covering; crown, helmet," and perhaps also from cognate Old Norse hjalmr, from Proto-Germanic *helmaz "protective covering," from PIE *kel- "to cover, to hide" (see cell). Italian elmo, Spanish yelmo are from Germanic.
helmet (n.): mid-15c., perhaps a diminutive of Old English helm "protection, covering; crown, helmet" (see helm (n.2)). But Barnhart says from Middle French helmet (Modern French heaume), diminutive of helme "helmet," from the same Germanic source as helm (n.2). "Middle English Dictionary" points to both without making a choice. "Old English helm never became an active term in the standard vocabulary of English." [Barnhart]
helmsman (n.): 1620s, from helm (n.1) + man (n.).
helot (n.): 1570s (with a capital -h-) "Spartan serf," from Greek Heilotes, plural of Heilos, popularly associated with Helos, Laconian town reduced to serfdom by Sparta, but perhaps related to Greek halonai "be captured." In extended use by 1820s.
help (v.): Old English helpan (class III strong verb; past tense healp, past participle holpen) "help, support, succor; benefit, do good to; cure, amend," from Proto-Germanic *helpan (cf. Old Norse hjalpa, Old Frisian helpa, Middle Dutch and Dutch helpen, Old High German helfan, German helfen), from PIE root *kelb- "to help" (cf. Lithuanian selpiu "to support, help").

Recorded as a cry of distress from late 14c. Sense of "serve someone with food at table" (1680s) is translated from French servir "to help, stead, avail," and led to helping "portion of food." Related: Helped (c.1300). The Middle English past participle holpen survives in biblical and U.S. dialectal use.
help (n.): Old English help (m.), helpe (f.) "assistance, succor;" see help (v.). Most Germanic languages also have the noun form, cf. Old Norse hjalp, Swedish hjälp, Old Frisian helpe, Dutch hulp, Old High German helfa, German Hilfe. Use of help as euphemism for "servant" is American English, 1640s, tied up in notions of class and race.
A domestic servant of American birth, and without negro blood in his or her veins ... is not a servant, but a 'help.' 'Help wanted,' is the common heading of advertisements in the North, when servants are required. [Chas. Mackay, "Life and Liberty in America," 1859].
Though help also meant "assistant, helper, supporter" in Middle English (c.1200).
helper (n.): mid-14c., agent noun from help (v.). Helpestre "a female helper" is recorded from c.1400. The Old English agent noun was helpend.
helpful (adj.): late 14c., from help (n.) + -ful. Related: Helpfully; helpfulness.
helping (n.): "aid, assistance," late 13c., from present participle of help (v.). Meaning “serving food” is from 1824; that of “a portion of food” is from 1883.
helpless (adj.): "unable to act for oneself," c.1200, from help (n.) + -less. Related: Helplessly; helplessness. In Middle English and later sometimes also "unable to give help, affording no help" (late 14c.), but this was never common.
helpmate (n.): "companion," 1715, altered from helpmeet, a ghost word, from the Biblical translation of Latin adjutorium simile sibi [Gen. ii:18] as "an help meet (i.e. fit) for him" (Hebrew 'ezer keneghdo), which already by 1673 was being printed as help-meet and mistaken for one word.
helpmeet (n.): as two words in the 1611 Bible, a noun-adjective phrase; hyphenated and mistaken as a modified noun by 1670s; see helpmate.
helter-skelter (adv.): also helter skelter, 1590s, perhaps from skelte "to hasten, scatter hurriedly," with the first element there merely for the sake of rhyme. As an adjective from 1785.
helve (n.): Old English helfe, hielfe "handle of an axe" or other tool or weapon, from Proto-Germanic *halb- (cf. Old Saxon helvi, Middle Dutch helf, Old High German halb "handle of an axe," Old High German helmo "tiller"); related to halter and helm (1), from PIE *kelp- "to hold, grasp." In Middle English, to holden the axe bi the helve (c.1200) meant "to take something by the right end."
Helvetian (adj.): "Swiss," 1550s, from Helvetia terra, Medieval Latin name of Switzerland, from Latin Helvetius "pertaining to the Helvetii," a Celtic people of ancient Gallia Lugdunensis.
hem (n.): Old English hem "a border," especially of cloth or a garment, from Proto-Germanic *hamjam (cf. Old Norse hemja "to bridle, curb," Swedish hämma "to stop, restrain," Old Frisian hemma "to hinder," Middle Dutch, German hemmen "to hem in, stop, hinder"), from PIE *kem- "to compress." Apparently the same root yielded Old English hamm, common in place names (where it means "enclosure, land hemmed in by water or high ground, land in a river bend"). In Middle English, hem also was a symbol of pride or ostentation.
If þei wer þe first þat schuld puplysch þese grete myracles of her mayster, men myth sey of hem, as Crist ded of þe Pharisees, þat þei magnified her owne hemmys. [John Capgrave, "Life of Saint Gilbert of Sempringham," 1451]
hem (interj.): late 15c., probably imitative of the sound of clearing the throat. Hem and haw first recorded 1786, from haw "hesitation" (1630s; see haw (v.)); hem and hawk attested from 1570s.
hem (v.): late 14c., "to provide (something) with a border or fringe" (surname Hemmer attested from c.1300), from hem (n.). Related: Hemmed; hemming. The phrase hem in "shut in, confine," first recorded 1530s.
hematite (n.): 1540s, haematites, from Middle French hematite (16c.), from Latin haematites, from Greek haimatites lithos "bloodlike stone," from haima (genitive haimatos) "blood" (see -emia). Earlier as emachite (late 14c.).
hemato-: also haemato-, word-forming element meaning "blood," from Greek haimato-, comb. form of haima (genitive haimatos) "blood" (see -emia).
hematoma (n.): 1826, from hemato- + -oma.
hemi-: word-forming element meaning "half," from Greek hemi- "half," from PIE root *semi-, which is the source of Sanskrit sami, Latin semi- (see semi-), Old High German sami- "half," and Old English sam-, denoting a partial or imperfect condition (see sandblind).
hemidemisemiquaver (n.): 1848, from hemi- + demi- + semi- + quaver (n.).
hemisphere (n.): late 14c., hemysperie, in reference to the celestial sphere, from Latin hemisphaerium, from Greek hemisphairion, from hemi- "half" (see hemi-) + sphaira "sphere" (see sphere). Spelling reformed 16c. Of the Earth, from 1550s; of the brain, 1804.
hemispheric (adj.): 1580s, from hemisphere + -ic.
hemistich (n.): "half a poetic line," 1570s, from Middle French hémistiche, from Latin hemistichium, from Greek hemistikhion "half-line, half-verse," from hemi- "half" (see hemi-) + stikhos "row, line of verse" (see stair).
hemline (n.): 1899, from hem (n.) + line (n.).
hemlock (n.): a poisonous plant, Old English (Kentish) hemlic, earlier hymlice, hymblice; of unknown origin. Liberman suggests from root hem- "poison," perhaps with the plant name suffix -ling or -ig. As the name of the poison derived from the plant, c.1600. The North American tree so called from 1776, from resemblance of its leaves to those of the plant.
hemo-: word-forming element meaning "blood," perhaps via Old French hemo-, Latin haemo-, from Greek haimo-, from haima "blood" (see -emia).
hemoglobin (n.): coloring matter in red blood stones, 1862, shortening of hæmatoglobin (1845), from Greek haimato-, comb. form of haima (genitive haimatos) "blood" (see -emia) + globulin, a type of simple protein, from globule, formerly a word for "corpuscle of blood."
hemophilia (n.): 1854 (in anglicized form hæmophily), from German hämophile, coined 1828 by German physician Johann Lucas Schönlein (1793-1864), from Greek haima "blood" (see -emia) + philia "to love" (see -philia), here with a sense of "tendency to."
hemophiliac: 1896 (adj.); 1897 (n.)., from hemophilia. Perhaps modeled on French hémophilique (1880).
hemophobia (n.): 1886, from hemo- "blood" + -phobia "fear."
hemorrhage (n.): c.1400, emorosogie (modern form by 17c.), from Latin haemorrhagia, from Greek haimorrhagia, from haimorrhages "bleeding violently," from haima "blood" (see -emia) + rhage "a breaking," from rhegnynai "to break, burst." Related: Hemorrhagic.
hemorrhage (v.): by 1882, from hemorrhage (n.). Related: Hemorrhaged; hemorrhaging.
Slang in Reports: B.I.D. for "Brought in Dead" and "Dotty" are, [Mr. Sidney Holland of London Hospital] considers, permissible expressions, but he draws the line at "fitting" and "hæmorrhaging." Only such terms, he says, should be used as outside doctors will understand. We would say that on a point of such odiously bad taste he might have been much more severe. [Lavinia L. Dock, "The American Journal of Nursing," 1906]
hemorrhoids (n.): plural of hemorrhoid; late 14c., emeroudis, from Old French emorroides (13c.), from Latin hæmorrhoidae, from Greek haimorrhoides (phlebes) "(veins) liable to discharge blood," plural of haimorrhois, from haima "blood" (see -emia) + rhoos "a stream, a flowing," from rhein "to flow" (see rheum). Related: Hemmorhoidal.
hemp (n.): Old English hænep "hemp, cannabis sativa," from Proto-Germanic *hanapiz (cf. Old Saxon hanap, Old Norse hampr, Old High German hanaf, German Hanf), probably a very early Germanic borrowing of the same Scythian word that became Greek kannabis (see cannabis). As the name of the fiber made from the plant, by c.1300. Slang sense of "marijuana" dates from 1940s; though scientific use for the narcotic derived from hemp dates to 1870.
hempen (adj.): "made of hemp," late 14c., from hemp + -en (2). In many figurative expressions 15c.-19c. it is in reference to the hangman's noose.
hemstitch (n.): also hem-stitch, 1821, from hem + stitch. As a verb by 1839. Related: Hemstitched; hemstitching.
hen (n.): Old English henn, from West Germanic *khannjo (cf. Old Frisian henn, Middle Dutch henne, Old High German henna), fem. of *han(e)ni "male fowl, cock" (cf. Old English hana "cock"), literally "bird who sings (for sunrise)," from PIE root *kan- "to sing" (see chant).

The original masculine word survives in German (Hahn "cock"), Swedish, Danish, etc.; extension to "female of any bird species" is early 14c. in English. Hen as slang for "woman" dates from 1620s; hence hen party "gathering of women," first recorded 1887. To be mad as a wet hen is from 1823, but the figure was used to indicate other states:
Some, on the contrary, are viciously opposite to these, who act so tamely and so coldly, that when they ought to be angry, to thunder and lighten, as one may say, they are no fuller of Heat, than a wet Hen, as the Saying is; .... ["Life of Mr. Thomas Betterton," London, 1710]

Orth. Out upon you for a dastardly Fellow; you han't the Courage of a wet Hen. ["A Sermon Preached at St. Mary-le-Bow, March 27, 1704"]
As wanton as a wet hen is in "Scots Proverbs" (1813). Among Middle English proverbial expressions was nice as a nonne hen "over-refined, fastidiously wanton" (c.1500); to singen so hen in snowe "sing miserably," literally "sing like a hen in snow" (c.1200). Hen's teeth as a figure of scarceness is attested by 1838.
hen-house (n.): 1510s, from hen + house (n.). As a place cheifly inhabited by or ruled by women, from 1785.
hence (adv.): late 13c., hennes, from Old English heonan "away, hence," from West Germanic *hin- (cf. Old Saxon hinan, Old High German hinnan, German hinnen); related to Old English her "here" (see here). With adverbial genitive -s. The modern spelling (mid-15c.) is phonetic, to retain the breathy -s- (cf. twice, pence). Original sense is "away from here;" of time, from late 14c.; meaning "from this (fact or circumstance)" first recorded 1580s.