intercoastal (adj.)
"within the coasts," 1927, from inter- + coastal.
intercom (n.)
1940, colloquial shortening of intercommunication (mid-15c., "discussion, conference;" see inter- + communication), which is attested from 1911 in reference to systems of linked telephones.
interconnect (v.)
1863, from inter- + connect. Related: Interconnected; interconnecting; interconnectedness; interconnection.
intercontinental (adj.)
1825, American English, from inter- + continental. Of missiles, from 1956.
intercostal (adj.)
"between the ribs," 1590s; see inter- + costal.
intercourse (n.)
mid-15c., "communication to and fro," from Old French entrecours "exchange, commerce," from Late Latin intercursus "a running between, intervention," from intercursus, past participle of intercurrere "to run between," from Latin inter- "between" (see inter-) + currere "to run" (see current (adj.)). Meaning "sexual relations" first recorded 1798, from earlier sense "social contact and relations" (1540s).
intercrural (adj.)
"between the thighs," or in madicine, "between leg-like structures," 1690s, from inter- + Latin crus "shin, shinbone leg; supports of a bridge."
interdepartmental (adj.)
also inter-departmental, 1861, from inter- + departmental.
interdependence (n.)
1822, from inter- + dependence.
interdependency (n.)
1838, from interdependent + -cy.
interdependent (adj.)
1817, from inter- + dependent. Related: Interdependently.
interdict (v.)
late 13c., from Old French entredit, past participle of entredire "forbid by decree," from Latin interdicere "interpose by speech, prohibit," from inter- "between" (see inter-) + dicere "to speak, to say" (see diction). Related: Interdicted; interdicting.
interdiction (n.)
mid-15c., enterdiccioun, from Latin interdictionem (nominative interdictio) "prohibition, interdiction," noun of action from past participle stem of interdicere (see interdict).
interdisciplinary (adj.)
1937, from inter- + disciplinary.
interest (n.)
mid-15c., "legal claim or right; concern; benefit, advantage;" earlier interesse (late 14c.), from Anglo-French interesse "what one has a legal concern in," from Medieval Latin interesse "compensation for loss," noun use of Latin interresse "to concern, make a difference, be of importance," literally "to be between," from inter- "between" (see inter-) + esse "to be" (see essence).

Compare German Interesse, from the same Medieval Latin source. Form in English influenced 15c. by French interest "damage," from Latin interest "it is of importance, it makes a difference," third person singular present of interresse. Financial sense of "money paid for the use of money lent" (1520s) earlier was distinguished from usury (illegal under Church law) by being in reference to "compensation due from a defaulting debtor." Meaning "curiosity" is first attested 1771. Interest group is attested from 1907; interest rate by 1868.
interest (v.)
"to cause to be interested," c.1600, earlier interesse (1560s), from the noun (see interest (n.)). Perhaps also from or influenced by interess'd, past participle of interesse.
interested (adj.)
"motivated by self-interest," 1705; "having an interest or stake (in something);" from past participle of interest (v.).
interesting (adj.)
1711, "that concerns, important," from interest (v.). Meaning "so as to excite interest" is from 1768. Related: Interestingly. Euphemistic phrase interesting condition, etc., "pregnant" is from 1748.
interface
1882 (n.), 1967 (v.), from inter- + face. Related: Interfaced; interfacing.
interfaith (adj.)
1921, from inter- + faith.
interfere (v.)
mid-15c., "to strike against," from Middle French enterferer "to strike each other," from entre- "between" (see entre-) + ferir "to strike," from Latin ferire "to knock, strike," related to Latin forare "to bore, pierce" (see bore (v.), and compare punch (v.), which has both the senses "to hit" and "to make a hole in"). Figurative sense of "to meddle with, oppose unrightfully" is from 1630s. Related: Interfered; interfering.
interference (n.)
1783, formed irregularly from interfere on model of difference, etc. Broadcasting and telephoning sense is from 1887. In chess from 1913; in U.S. football from 1894.
interferometer (n.)
"instrument for measuring the interference of light waves," 1897, a hybrid from interfere + meter (3).
interferon (n.)
1957, coined in English, so called because it "interferes" with the reduplication of viruses. From interfere + subatomic particle suffix -on.
intergalactic (adj.)
1928, from inter- + galactic.
intergenerational (adj.)
1964, from inter- + generation + -al (1).
interglacial (adj.)
1867, from German, coined 1865 by Swiss naturalist Oswald Heer (1809-1883); see inter- + glacial.
interim (n.)
1540s, from Latin interim (adv.) "in the meantime, meanwhile," originally "in the midst of that," from inter- "between" (see inter-) + im, ancient adverb from stem of pronoun is "this, that."
interior (adj.)
late 15c., from Middle French intérieur and directly from Latin interior "inner, interior, middle," comparative adjective of inter "within" (see inter-). Meaning "of the interior parts of a country" is from 1777; meaning "internal affairs of a country or state" (as in U.S. Department of the Interior) is from 1838. Interior decoration first attested 1807. Interior design from 1927.
interior (n.)
"part of a country distant from the coast," 1796, from interior (adj.); meaning "inside of a building or room" is from 1829.
interiority (n.)
1701, from interior + -ity.
interjacent (adj.)
1590s, from Latin interiacentem (nominative interiacens) "lying between," present participle of interiacere "to lie between," from inter- (see inter-) + iacere (see jet (v.)).
interject (v.)
1570s, back-formation from interjection or else from Latin interiectus, past participle of intericere "to throw between, insert, interject" (see interjection). Related: Interjected; interjecting.
interjection (n.)
early 15c., from Middle French interjection (Old French interjeccion, 13c.), from Latin interiectionem (nominative interiectio) "a throwing or placing between," noun of action from past participle stem of intericere, from inter- "between" (see inter-) + -icere, comb. form of iacere "to throw" (see jet (v.)).
interlace (v.)
late 14c., from Middle French entrelacer, from entre- (see entre-) + lacer (see lace). Television sense is from 1927. Related: Interlaced; interlacing. The noun is 1904, from the verb.
interlard (v.)
early 15c., "to mix with alternate layers of fat" (before cooking), from Middle French entrelarder, from entre- "between" (see inter-) + larder "to lard," from Old French lard "bacon fat" (see lard (n.)). Figurative sense of "diversify with something intermixed" first recorded 1560s. Related: Interlarded; interlarding.
interleague (adj.)
also inter-league, by 1917 in a U.S. baseball sense, from inter- + league. Earlier (1580s) as a verb.
interline (v.)
c.1400, "make corrections or insertions between the lines of (a document)," from inter- + line; perhaps modeled on Medieval Latin interlineare. Related: Interlined; interlining.
interlinear (adj.)
late 14c., from Medieval Latin interlinearis "that which is between the lines," from inter- (see inter-) + Latin linearis (see linear).
interlock (v.)
1630s, from inter- + lock. Related: Interlocked; interlocking. As a noun, attested by 1874.
interlocution (n.)
1530s, from Latin interlocutionem (nominative interlocutio) "a speaking between, interlocution," noun of action from past participle stem of interloqui (see interlocutor).
interlocutor (n.)
1510s, agent noun from Latin interlocut-, past participle stem of interloqui "interrupt," from inter- "between" (see inter-) + loqui "to speak" (see locution). Related: Interlocutory.
interlope (v.)
early 17c., a back-formation from interloper, or else from inter- + lope (see interloper). Related: Interloped; interloping.
interloper (n.)
1590s, enterloper, "unauthorized trader trespassing on privileges of chartered companies," probably a hybrid from inter- "between" + -loper (from landloper "vagabond, adventurer," also, according to Johnson, "a term of reproach used by seamen of those who pass their lives on shore"); perhaps a dialectal form of leap, or from Middle Dutch loper "runner, rover," from lopen "to run," from Proto-Germanic *hlaupan "to leap" (see leap (v.)). General sense of "self-interested intruder" is from 1630s.
interlude (n.)
c.1300, from Medieval Latin interludium "an interlude," from Latin inter- "between" (see inter-) + ludus "a play" (see ludicrous). Originally farcical episodes introduced between acts of long mystery plays; transferred sense of "interval in the course of some action" is from 1751.
intermarriage (n.)
1570s, from inter- + marriage.
intermarry (v.)
1570s, "to marry one another," from inter- + marry. Meaning "to marry across families, castes, tribes, etc." is from 1610s. Related: Intermarried; intermarrying.
intermeddle (v.)
late 14c., from Latin inter- (see inter-) + Anglo-French medler (see meddle (v.)).
intermediary
1788 (adj.); 1791 (n.), from French intermédiaire (17c.), from Medieval Latin intermedium, from Latin intermedius (see intermediate).
intermediate (adj.)
early 15c., from Medieval Latin intermediatus "lying between," from Latin intermedius "that which is between," from inter- "between" (see inter-) + medius "in the middle" (see medial (adj.)).