interface n.

word-forming element used freely in English, "between, among, during," from Latin inter (prep., adv.) "among, between, betwixt, in the midst of" (also used extensively as a prefix), from PIE *enter "between, among" (source also of Sanskrit antar, Old Persian antar "among, between," Greek entera (plural) "intestines," Old Irish eter, Old Welsh ithr "among, between," Gothic undar, Old English under "under"), a comparative of root *en "in."

A living prefix in English from 15c. and used with Germanic as well as Latinate words. Spelled entre- in French; most words borrowed into English in that form were re-spelled 16c. to conform with Latin except entertain, enterprise. In Latin, spelling shifted to intel- before -l-, hence intelligence, etc.

c. 1300, "the human face, a face; facial appearance or expression; likeness, image," from Old French face "face, countenance, look, appearance" (12c.), from Vulgar Latin *facia (source also of Italian faccia), from Latin facies "appearance, form, figure," and secondarily "visage, countenance," which probably is literally "form imposed on something" and related to facere "to make" (from PIE root *dhe- "to set, put").

Replaced Old English andwlita "face, countenance" (from root of wlitan "to see, look") and ansyn, ansien, the usual word (from the root of seon "see"). Words for "face" in Indo-European commonly are based on the notion of "appearance, look," and are mostly derivatives from verbs for "to see, look" (as with the Old English words, Greek prosopon, literally "toward-look," Lithuanian veidas, from root *weid- "to see," etc.). But in some cases, as here, the word for "face" means "form, shape." In French, the use of face for "front of the head" was given up 17c. and replaced by visage (older vis), from Latin visus "sight."

From late 14c. as "outward appearance (as contrasted to some other reality);" also from late 14c. as "forward part or front of anything;" also "surface (of the earth or sea), extent (of a city)." Typographical sense of "part of the type which forms the letter" is from 1680s.

Whan she cometh hoom, she raumpeth in my face And crieth 'false coward.' [Chaucer, "Monk's Tale"]

Face to face is from mid-14c. Face time is attested from 1990. To lose face "lose prestige" (1835), is from Chinese tu lien; hence also save face (1898; see save). To show (one's) face "make or put in an appearance" is from mid-14c. (shewen the face). To make a face "change the appearance of the face in disgust, mockery, etc." is from 1560s. Two faces under one hood as a figure of duplicity is attested from mid-15c.

Two fases in a hode is neuer to tryst. ["Awake lordes," 1460]