intertidal (adj.)

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.

"of, pertaining to, or cause by tides or a tide," 1807, a hybrid formation from tide (n.) + Latin-derived suffix -al (1). A tidal wave (1819) properly is high water caused by movements of the tides; its use for "great ocean inundation caused by an earthquake, etc." is recorded by 1868. This now tends to be called a tsunami.