Online Etymology Dictionary

prophylactic (adj.): 1570s, originally of medicines, "that tends to prevent disease," from Middle French prophylactique (16c.) and directly as a Latinized borrowing of Greek prophylaktikos "precautionary," from prophylassein "keep guard before, ward off, be on one's guard," from pro- "before" (see pro-) + phylassein, Ionic variant of phylattein "to watch over, to guard," but also "cherish, keep, remain in, preserve" (see phylactery).

The noun is first recorded 1640s, "a medicine or treatment to prevent disease;" meaning "condom" is from 1943, replacing earlier preventive (1822), preventative (1901). Condoms originally were used more to thwart contagious disease than to prevent pregnancy.
prophylaxis (n.): "preventive treatment of disease," 1746, Modern Latin, from Greek pro (see pro-) + phylaxis "a watching, guarding" (see prophylactic).
propinquity (n.): late 14c., "nearness in relation, kinship," later also "physical nearness" (early 15c.), from Old French propinquite (13c.) and directly from Latin propinquitatem (nominative propinquitas) "nearness, vicinity; relationship, affinity," from propinquus "near, neighboring," from prope "near" (enlarged from PIE *pro "before;" see pro-) + suffix -inquus.
Nothing propinks like propinquity [Ian Fleming, chapter heading, "Diamonds are Forever," 1956; phrase popularized 1960s by U.S. diplomat George Ball]
propitiate (v.): 1580s, a back-formation from propritiation and in part from propitiate (adj.), from Latin propitiatus, past participle of propitiare "appease, propitiate" (see propitiation). Related: Propitiated; propitiating; propitiatingly; propitiable (1550s).
propitiation (n.): late 14c., from Late Latin propitiationem (nominative propitiatio) "an atonement," noun of action from past participle stem of Latin propitiare "appease, propitiate," from propitius "favorable, gracious, kind, well-disposed," from pro- "forward" (see pro-) + stem related to petere "to make for, go to; seek, strive after; ask for, beg, beseech, request" (see petition (n.)).

The sense in Latin is perhaps because the word originally was religious, literally "a falling or rushing toward," hence "eager," and, of the gods, "well-disposed." Earliest recorded form of the word in English is propitiatorium "the mercy seat, place of atonement" (c.1200), translating Greek hilasterion.
propitiatory: c.1300 (n.) "the mercy seat," from Late Latin propitiatorium (translating Greek hilasterion in Bible); noun use of neuter singular of propitiatorius "atoning, reconciling," from propitiatus, past participle of propitiare (see propitiation). As an adjective in English from 1550s.
propitious (adj.): mid-15c., from Anglo-French propicius, Old French propicius "gracious, favorable, useful" (12c., Modern French propice) and directly from Latin propitius "favorable, kind, gracious, well-disposed" (see propitiation). Earlier English form was propice, from Old French propice. Related: Propitiously.
propone (v.): "propose," late 14c., from Latin proponere "to put forth" (see propound). Related: Proponed; proponing; proponement.
proponent (n.): 1580s, "one who brings forth a proposition or argument," from Latin proponentem (nominative proponens), present participle of proponere "put forward" (see propound). In part also a native formation from propone. As an adjective from 1680s.
proport (v.): late 14c., from Old French proporter (12c.), variant of porporter (see purport).
proportion (n.): late 14c., "due relation of one part to another," also "size, extent; compartative relation in size, degree, number, etc.," from Old French proporcion "measure, proportion" (13c.), from Latin proportionem (nominative proportio) "comparative relation, analogy," from phrase pro portione "according to the relation" (of parts to each other), from pro "for" (see pro-) + ablative of *partio "division," related to pars (see part (n.)). Phrase out of proportion attested by 1670s.
My fortunes [are] as ill proportioned as your legs. [John Marston, "Antonio and Mellida," 1602]
proportion (v.): "to adjust or regulate the proportions of," late 14c., from proportion (n.) and in part from Middle French proporcioner and directly from Medieval Latin proportionare. Related: Proportioned; proportioning.
proportional (adj.): late 14c. (implied in proportionally), from Late Latin proportionalis "pertaining to proportions," from proportio (see proportion). Related: Proportionally.
proportionality (n.): 1560s, from French proportionalité (14c.) or directly from Medieval Latin proportionalitas, from proportio (see proportion).
proportionate (adj.): late 14c., "of proper proportion," from Medieval Latin proportionatus "proportioned," past participle of proportionare (see proportion (n.)). Related: Proportionately.
proposal (n.): 1650s, from propose + -al (2); specific sense of "offer of marriage" is from 1749.
propose (v.): mid-14c., from Old French proposer "propose, advance, suggest" (12c.), from pro- "forth" (see pro-) + poser "put, place" (see pose (v.1)). Meaning "make an offer of marriage" is first recorded 1764. Related: Proposed; proposing. Cf. also propone, which coexisted with this word for a time.
proposition (n.): mid-14c., "a setting forth as a topic for discussion," from Old French proposicion "proposal, submission, (philosophical) proposition" (12c.), from Latin propositionem (nominative propositio) "a setting forth, statement, a presentation, representation; fundamental assumption," noun of action from past participle stem of proponere (see propound). Meaning "action of proposing something to be done" is from late 14c. General sense of "matter, problem, undertaking" recorded by 1877. Related: Propositional.
proposition (v.): 1914, from proposition (n.); specifically of sexual favors from 1936. Related: Propositioned; propositioning.
propound (v.): late 16c. variant of Middle English proponen "to put forward" (late 14c.), from Latin proponere "put forth, set forth, lay out, display, expose to view," figuratively "set before the mind; resolve; intend, design," from pro- "before" (see pro-) + ponere "to put" (see position (n.)). Perhaps influenced in form by compound, expound. Related: Propounded; propounding.
proprietary (adj.): mid-15c., "possessing worldly goods in excess of a cleric's needs," from Medieval Latin proprietarius "owner of property," noun use of Late Latin adjective proprietarius "of a property holder," from Latin proprietas "owner" (see property). Meaning "held in private ownership" is first attested 1580s. The word was used earlier in English as a noun meaning "proprietor," also "worldly person" (c.1400), from a noun use in French and Medieval Latin.
proprietor (n.): 1630s, "owner, by royal grant, of an American colony," probably from proprietary (n.) in sense "property owner" (late 15c., see proprietary). In general sense of "one who holds something as property" it is attested from 1640s.
propriety (n.): mid-15c., "proper character, disposition," from Old French proprieté "individuality, peculiarity; property" (12c.), from Latin proprietatem (nominative proprietas) "appropriateness," also "ownership" (see property). Meaning "fitness, appropriateness" is attested from 1610s; sense of "conformity to good manners" is from 1782.
proprioception (n.): 1906, from proprioceptor, from Latin proprius "own" (see proper) + reception. Coined by English neurophysiologist C.S. Sherrington (1857-1952). Related: Proprioceptive; proprioceptor.
propulsion (n.): 1610s, "expulsion," noun of action formed from propuls-, past participle stem of Latin propellere "to propel" (see propel). Meaning "act of driving forward, propulsive force" first attested 1799.
propulsive (adj.): 1640s, from propuls-, past participle stem of Latin propellere "to propel" (see propel) + -ive.
prorate (v.): also pro-rate, "divide proportionally," 1860, American English, verb derived from Latin pro rata (parte) (see pro rata). Related: Prorated; prorating.
proration (n.): 1893, noun of action from prorate (v.).
prorogue (v.): early 15c., "to prolong, extend," from Old French proroger, proroguer (14c.), from Latin prorogare, literally "to ask publicly," from pro "before" (see pro-) + rogare "to ask" (see rogation). Perhaps the original sense in Latin was "to ask for public assent to extending someone's term in office." Legislative meaning "discontinue temporarily" is attested from mid-15c. Related: Prorogation.
prosaic (adj.): 1650s, "having to do with prose," from Middle French prosaique and directly from Medieval Latin prosaicus "in prose" (16c.), from Latin prosa "prose" (see prose). Meaning "having the character of prose (in contrast to the feeling of poetry)" is by 1746; extended sense of "ordinary" is by 1813, both from French.
proscenium (n.): c.1600, "stage of an ancient theater," from Latin proscaenium, from Greek proskenion "the space in front of the scenery," also "entrance of a tent," from pro "in front" (see pro-) + skene "stage, tent, booth" (see scene). Modern sense of "space between the curtain and the orchestra" is attested from 1807.
prosciutto (n.): Italian spiced ham, 1911, from Italian, alteration (probably by influence of prosciugato "dried") of presciutto, from pre-, intensive prefix + -sciutto, from Latin exsuctus "lacking juice, dried up," past participle of exsugere "suck out, draw out moisture," from ex- "out" (see ex-) + sugere "to suck" (see sup (v.2)).
proscribe (v.): early 15c., "write before, prefix," from Latin proscribere "publish in writing" (literally "write in front of"), including senses of "publish as having forfeited one's property, condemn, outlaw before the world," from pro- "before" (see pro-) + scribere "to write" (see script). Meaning "prohibit as wrong or dangerous" first recorded 1620s.
proscription (n.): late 14c., "decree of condemnation, outlawry," from Latin proscriptionem (nominative proscriptio) "a public notice (of sale); proscription, outlawry, confiscation," noun of action from past participle stem of proscribere (see proscribe).
proscriptive (adj.): 1757, from Latin proscript-, past participle stem of proscribere (see proscribe) + -ive. Related: Proscriptively.
prose (n.): c.1300, "story, narration," from Old French prose (13c.), from Latin prosa oratio "straightforward or direct speech" (without the ornaments of verse), from prosa, fem. of prosus, earlier prorsus "straightforward, direct," from Old Latin provorsus "(moving) straight ahead," from pro- "forward" (see pro-) + vorsus "turned," past participle of vertere "to turn" (see verse).
"Good prose, to say nothing of the original thoughts it conveys, may be infinitely varied in modulation. It is only an extension of metres, an amplification of harmonies, of which even the best and most varied poetry admits but few." [Walter Savage Landor, "Imaginary Conversations"]
Meaning "prose writing; non-poetry" is from mid-14c. The sense of "dull or commonplace expression" is from 1680s, out of earlier sense "plain expression" (1560s). Those who lament the want of an English agent noun to correspond to poet might try prosaist (1776), proser (1620s), or Frenchified prosateur (1880), though the first two in their day also acquired in English the secondary sense "dull writer."
prosecute (v.): early 15c., "follow up, pursue" (some course or action), from Latin prosecutus, past participle of prosequi "follow after, accompany; chase, pursue; attack, assail, abuse" (see pursue). Meaning "bring to a court of law" is first recorded 1570s. Meaning "go into detail" is from 1530s.
prosecution (n.): 1560s, "action of pursuing," from Middle French prosecution (late 13c.) and directly from Late Latin prosecutionem (nominative prosecutio) "a following," noun of action from past participle stem of prosequi (see prosecute). Meaning "legal action" is from 1630s.
prosecutor (n.): 1590s, from Medieval Latin prosecutor, agent noun from prosequi (see prosecute). Specific legal sense of "one who brings a case in a court of law" is from 1620s; earlier such a person was a promoter (late 15c.). Related: Prosecutorial.
proselyte (n.): late 14c., from Old French proselite (13c., Modern French prosélyte), from Late Latin proselytus, from Greek proselytos "convert (to Judaism), stranger, one who has come over," noun use of adjective meaning "having arrived," from second aorist stem of proserkhesthai "to come or go; surrender; associate with," from proti "toward" + root of eleusesthai "to be going to come," from PIE *elu-to-, from root *leudh- "to go." Originally in English "a Gentile converted to Judaism" (late 14c.).
proselytise (v.): chiefly British English spelling of proselytize (q.v.). For suffix, see -ize. Related: Proselytised; proselytising.
proselytism (n.): 1650s, from proselyte + -ism.
proselytization (n.): 1846, from proselytize + -ation.
proselytize (v.): 1670s, "to make proselytes," from proselyte + -ize. Related: Proselytized; proselytizing.
proselytizer (n.): 1811, agent noun from proselytize.
Proserpina: daughter of Ceres and wife of Pluto, Latin (or Etruscan) modification of Greek Persephone, perhaps influenced by Latin proserpere "to creep forth" on notion of the germination of plants.
prosify (v.): 1774, from prose + -ify. Related: Prosified; prosifying.
prosiness (n.): 1814, from prosy + -ness.
prosit (interj.): 1846, toast or expression wishing good health (from 16c., famously a drinking pledge by German students), Latin, literally "may it advantage (you)," third person singular present subjunctive of prodesse "to do good, be profitable" (see proud).
prosodemic (adj.): 1964, with -ic + prosodeme (1940), from Greek proso-, probably related to pros "toward, to, at, against, near."