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Latin inter (prep., adv.) "among, between, betwixt, in the midst of," from PIE *enter "between, among" (cf. 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 *en "in" (see in). Also in certain Latin phrases in English, such as inter alia "among other things." A living prefix in English from 15c. Spelled entre- in French, most words borrowed into English in that form were re-spelled 16c. to conform with Latin except entertain, enterprise.
Between; among: interdental.
In the midst of; within: interoceptor.
A prefix meaning "between" or "among," as in interplanetary, located between planets.