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.
early 15c., "act of communicating, act of imparting, discussing, debating, conferring," from Old French comunicacion (14c., Modern French communication) and directly from Latin communicationem (nominative communicatio) "a making common, imparting, communicating; a figure of speech," noun of action from past-participle stem of communicare "to share, divide out; communicate, impart, inform; join, unite, participate in," literally "to make common," related to communis "common, public, general" (see common (adj.)). Meaning "that which is communicated" is from late 15c.; meaning "means of communication" is from 1715. Related: Communications; communicational.