interterritorial (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.

late 14c., "land under the jurisdiction of a town, state, etc.," probably from Latin territorium "land around a town, domain, district," from terra "earth, land" (from PIE root *ters- "to dry") + -orium, suffix denoting place (see -ory). Sense of "any tract of land, district, region" is first attested c. 1600. Specific U.S. sense of "organized self-governing region not yet a state" is from 1799. Of regions defended by animals from 1774.

"Since -torium is a productive suffix only after verbal stems, the rise of terri-torium is unexplained" [Michiel de Vaan, "Etymological Dictionary of Latin and the other Italic Languages"]. An alternative theory, somewhat supported by the vowels of the original Latin word, suggests derivation from terrere "to frighten" (see terrible); thus territorium would mean "a place from which people are warned off."

suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).