interamnian (adj.) Look up interamnian at Dictionary.com
"between two rivers" (usually, if not exclusively, with reference to Mesopotamia), 1774, from Late Latin interamnius, from inter "between" (see inter-) + amnis "a river," a word perhaps of Celtic origin (see afanc).
interblend (v.) Look up interblend at Dictionary.com
"intermingle," 1823, from inter- + blend (v.). Related: Interblended; interblending.
interbreed (v.) Look up interbreed at Dictionary.com
1803 (transitive) "to breed by crossing species or varieties," from inter- + breed (v.). Intransitive sense of "procreate with one of a different species" is from 1825. Related: Interbred; interbreeding.
intercalary (adj.) Look up intercalary at Dictionary.com
"inserted into the calendar," 1610s, from Latin intercalarius "intercalary, of an intercalary month," from intercalare "proclaim an intercalary day" (see intercalate). General sense of "interpolated" is attested from 1798.
intercalate (v.) Look up intercalate at Dictionary.com
"to insert a day into the calendar," 1610s, from Latin intercalatus, past participle of intercalare "to proclaim the insertion of an intercalary day," from inter- "between" (see inter-) + calare "to call" (an intercalary day; see calendar). Related: Intercalated; intercalating.

A necessary process in the Roman calendar to balance the solar and lunar aspects of it. Intercalation was done after Feb. 23 or 24 (the terminalia), every two or four years. Twenty-seven days were intercalated, making a full intercalary month (which included the last four or five days of Februarius), known as mensis intercalaris (and also known, according to Plutarch, as Mercedonius). No one now knows why the intercalation was done in the middle of February rather than after its end, unless it was because the important festivals at the end of that month (Regifugium and Equirra) were closely associated with holidays in early March. After Caesar's reform (46 B.C.E.) the only intercalary day is Feb. 29 every four years.
intercalation (n.) Look up intercalation at Dictionary.com
1570s, from Latin intercalationem (nominative intercalatio) "insertion of an intercalary day," noun of action from past participle stem of intercalare "proclaim an intercalary day" (see intercalate). The general sense "insertion of any addition into an existing series" is from 1640s.
intercede (v.) Look up intercede at Dictionary.com
1570s, "to come between in space or time" (obsolete); c. 1600, "to interpose on behalf of another," a back-formation from intercession, or else from Latin intercedere "intervene, come between, be between" (in Medieval Latin "to interpose on someone's behalf"), from inter- "between" (see inter-) + cedere "go" (see cede). Related: Interceded; interceding.
intercept (n.) Look up intercept at Dictionary.com
"that which is intercepted," from intercept (v.). From 1821 of a ball thrown in a sport; 1880 in navigation; 1942 in reference to secret messages.
intercept (v.) Look up intercept at Dictionary.com
c. 1400, "to cut off" (a line), "prevent" (the spread of a disease), from Latin interceptus, past participle of intercipere "take or seize between, to seize in passing," from inter- "between" (see inter-) + -cipere, comb. form of capere "to take, catch," from PIE root *kap- "to grasp" (see capable). Related: Intercepted; intercepting.
interception (n.) Look up interception at Dictionary.com
early 15c., "action of intercepting" (the flow of a bodily fluid), from Latin interceptionem (nominative interceptio) "a seizing, taking away," noun of action from past participle stem of intercipere (see intercept (v.)). Specific football/rugby sense is attested by 1897. Meaning "action of closing in on and destroying an enemy aircraft, etc." is recorded from 1939.
interceptor (n.) Look up interceptor at Dictionary.com
1590s, from Latin interceptor "interceptor, usurper, embezzler," agent noun from intercipere (see intercept (v.)). As a type of fast fighter aircraft, from 1930. Intercepter is attested from c. 1600.
intercession (n.) Look up intercession at Dictionary.com
early 15c., "act of interceding;" c. 1500, "intercessory prayer, a pleading on behalf of oneself or another," from Latin intercessionem (nominative intercessio) "a going between, coming between, mediation," noun of action from past participle stem of intercedere "intervene, come between, be between" (in Medieval Latin "to interpose on someone's behalf;" see intercede). The sense "pleading on behalf of another" developed in Christianity.
intercessor (n.) Look up intercessor at Dictionary.com
"one who pleads or intervenes on behalf of another," late 15c., from a specific Christian use of Latin intercessor "one who intervenes, a mediator," agent noun from intercedere (see intercede). Related: Intercessory.
interchange (v.) Look up interchange at Dictionary.com
late 14c., enterchaungen, "to give and receive reciprocally; to alternate, put each in place of the other" (trans.), also "change reciprocally" (intrans.), from Old French entrechangier "interchange, exchange," from entre- "between" (see inter-) + changier "to change" (see change (v.)). Related: Interchanged; interchanging.
interchange (n.) Look up interchange at Dictionary.com
early 15c., "an exchange, act of exchanging reciprocally," from Old French entrechange, from entrechangier (see interchange (v.)). Meaning "alternate succession" is from 1550s. In reference to a type of road junction, 1944.
interchangeability (n.) Look up interchangeability at Dictionary.com
1763; see interchangeable + -ity.
interchangeable (adj.) Look up interchangeable at Dictionary.com
late 14c., entrechaungeable, "mutual, reciprocal," from inter- + changeable. Meaning "capable of being used in place of each other" is from 1560s. Related: Interchangeably.
intercoastal (adj.) Look up intercoastal at Dictionary.com
"within the coasts," 1927, from inter- + coastal.
intercollegiate (adj.) Look up intercollegiate at Dictionary.com
1873, from inter- + collegiate.
intercom (n.) Look up intercom at Dictionary.com
"radio or telephone intercommunication system," 1937, colloquial shortening of intercommunication, which is attested from 1911 in reference to systems of linked telephones.
intercommunicate (v.) Look up intercommunicate at Dictionary.com
1580s, "communicate reciprocally," from inter- + communicate (v.) or else from Medieval Latin intercommunicatus, past participle of intercommunicare.
intercommunication (n.) Look up intercommunication at Dictionary.com
mid-15c., "discussion, conference," from Anglo-Latin intercommunicationem; see inter- + communication). Attested from 1881 in reference to systems of linked telephones.
intercommunion (n.) Look up intercommunion at Dictionary.com
1749, "intimate intercourse, fellowship," from inter- "between" + communion (n.).
interconnect (v.) Look up interconnect at Dictionary.com
1863, from inter- + connect (v.). Related: Interconnected; interconnecting.
interconnectedness (n.) Look up interconnectedness at Dictionary.com
1873, noun of state from past participle of interconnect + -ness. Interconnection is attested from 1827.
intercontinental (adj.) Look up intercontinental at Dictionary.com
1825, American English, from inter- "between" + continental (adj.). Of missiles, from 1956.
intercostal (adj.) Look up intercostal at Dictionary.com
"between the ribs," 1590s; see inter- + costal.
intercourse (n.) Look up intercourse at Dictionary.com
mid-15c., "communication to and fro," ("In early use exclusively with reference to trade" [OED]), from Old French entrecors "exchange, commerce, communication" (12c., Modern French entrecours), from Late Latin intercursus "a running between, intervention," in Medieval Latin "intercommunication," from intercursus, past participle of intercurrere "to run between, intervene, mediate," from Latin inter- "between" (see inter-) + currere "to run" (see current (adj.)).

Sense of "frequent and habitual meeting and contact, social communication between persons" is from 1540s. Meaning "mental or spiritual exchange or intercommunication" is from 1560s. Meaning "sexual relations" (1798) probably is a shortening of euphemistic sexual intercourse (1771) with intercourse in its sense "social contact and relations."
intercrural (adj.) Look up intercrural at Dictionary.com
"between the thighs," or in medicine, "between leg-like structures," 1690s, from inter- "between" + Latin crus "shin, shank, (lower) leg; supports of a bridge," from Proto-Italic *krus-, which is of uncertain origin.
interdepartmental (adj.) Look up interdepartmental at Dictionary.com
also inter-departmental, 1861, from inter- + departmental.
interdependence (n.) Look up interdependence at Dictionary.com
1816 (Coleridge), from inter- + dependence.
interdependency (n.) Look up interdependency at Dictionary.com
1830, from interdependent + -cy.
interdependent (adj.) Look up interdependent at Dictionary.com
1817 (Coleridge), from inter- + dependent. Related: Interdependently.
interdict (v.) Look up interdict at Dictionary.com
c. 1300, enterditen, "to place under ban of the Church, excommunicate," from Old French entredit (Modern French interdit), past participle of entredire "forbid by decree, excommunicate," from Latin interdicere "interpose by speech, prohibit, forbid," from inter- "between" (see inter-) + dicere "to speak, to say" (see diction). General sense "forbid, prohibit" in English is from early 15c. Related: Interdicted; interdicting; interdictory.
interdiction (n.) Look up interdiction at Dictionary.com
mid-15c., enterdiccioun, from Latin interdictionem (nominative interdictio) "a prohibiting, a forbidding," noun of action from past participle stem of interdicere (see interdict).
interdisciplinary (adj.) Look up interdisciplinary at Dictionary.com
1937, from inter- + disciplinary.
interest (n.) Look up interest at Dictionary.com
mid-15c., "legal claim or right; a concern; a benefit, advantage, a being concerned or affected (advantageously)," from Old French interest "damage, loss, harm" (Modern French intérêt), from noun use of Latin interest "it is of importance, it makes a difference," third person singular present of interresse "to concern, make a difference, be of importance," literally "to be between," from inter- "between" (see inter-) + esse "to be" (see essence). The sense development to "profit, advantage" in French and English is not entirely clear.

The earlier Middle English word was 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 (compare German Interesse, from the same Medieval Latin source).

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." Sense of "personal or selfish consideration" is from 1620s. Meaning "business in which several people are interested" is from 1670s. Meaning "curiosity, feeling that something concerns one, appreciative or sympathetic regard" is first attested 1771. Interest group is attested from 1907; interest rate by 1868.
interest (v.) Look up interest at Dictionary.com
"cause to be interested, engage the attention of," 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.) Look up interested at Dictionary.com
1660s, "characterized by concern or sympathy," past-participle adjective from interest (v.). From 1828 as "having an interest or stake (in something);" sense "motivated by self-interest" (1705) is perhaps a back-formation from disinterested. Related: Interestedness.
interesting (adj.) Look up interesting at Dictionary.com
1711, "that concerns, important" (archaic), present-participle adjective from interest (v.). Meaning "engaging the attention, so as to excite interest" is from 1751. Related: Interestingly. Euphemistic phrase interesting condition, etc., "pregnant" is from 1748.
interface (n.) Look up interface at Dictionary.com
1874, "a plane surface regarded as the common boundary of two bodies," from inter- + face (n.). Modern use is perhaps a c. 1960 re-coinage; McLuhan used it in the sense "place of interaction between two systems" (1962) and the computer sense "apparatus to connect two devices" is from 1964. As a verb from 1967. Related: Interfaced; interfacing.
interfacial (adj.) Look up interfacial at Dictionary.com
1837, of crystals, from inter- "between" + facial (adj.).
interfaith (adj.) Look up interfaith at Dictionary.com
1921, from inter- + faith.
interfere (v.) Look up interfere at Dictionary.com
formerly also enterfere, mid-15c., "to strike against," from Middle French enterferir "exchange blows, 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. Modern French interférer is from English.
interference (n.) Look up interference at Dictionary.com
1783, "intermeddling," from interfere on model of difference, etc. In physics, in reference to the mutual action of waves on each other, from 1802, coined in this sense by English scientist Dr. Thomas Young (1773-1829). Telephoning (later broadcasting) sense is from 1887. In chess from 1913; in U.S. football from 1894.
interferometer (n.) Look up interferometer at Dictionary.com
"instrument for measuring the interference of light waves," 1897, a hybrid from interfere + -meter. Compare interferential (1867), coined on the model of differential. Related: Interferometric; interferometry.
interferon (n.) Look up interferon at Dictionary.com
animal protein, 1957, coined in English from interfere + subatomic particle suffix -on; so called because it "interferes" with the reduplication of viruses.
interflow (n.) Look up interflow at Dictionary.com
"a flowing into each other," 1839, from inter- + flow (n.).
interfold (v.) Look up interfold at Dictionary.com
1570s, from inter- + fold (v.). Related: Interfolded; interfolding.
intergalactic (adj.) Look up intergalactic at Dictionary.com
1928, in reference to galaxies as presently understood, from inter- + galactic. The word itself was in use by 1901, when galaxies were thought to be a sort of nebulae.