interdependence (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.

early 15c., dependaunce, "consequence, result, relation of a conclusion to a premise or an effect to a cause," from Old French dépendance (from dependre; see depend) and from Medieval Latin dependentia. Originally also dependance (which is the older of the two modern spellings), depending whether the writer had French or Latin foremost in mind; the Latin form gradually predominated, and after c. 1800 the spelling dependance is rare. For discussion, see dependant (n.).

From mid-15c. as "state of deriving existence, support, or direction from another." From 1620s as "reliance, confidence, trust." Literal meaning "fact of hanging from something" (1690s) was rare and is obsolete.