interplay 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.

Middle English pleie, from Old English plega (West Saxon), plæga (Anglian) "quick motion; recreation, exercise, any brisk activity" (the latter sense preserved in swordplay -- Old English sweordplegan -- etc.), from or related to Old English plegan (see play (v.)).

By early Middle English it could mean variously, "a game, a martial sport, activity of children, joke or jesting, revelry, sexual indulgence." Of physical things, "rapid, brisk, or light movement," by 1620s.

Meaning "dramatic performance" is attested by early 14c., perhaps late Old English. Meaning "free or unimpeded movement, liberty and room for action," of mechanisms, etc., is from 1650s. The meaning "activity, operation" (1590s) is behind expressions such as in full play, come into play. The sporting sense of "the playing of a game" is attested from mid-15c.; that of "specific maneuver or attempt" is from 1868.

The U.S. slang meaning "attention, publicity" is by 1929. To be in play (of a hit ball, etc.) is from 1788. Play-by-play in reference to running commentary on a game is attested from 1927. Play on words "pun" is from 1798. Play-money is attested from 1705 as "money won in gambling," by 1920 as "pretend money."