ento- Look up ento- at Dictionary.com
word-forming element used chiefly in biology and meaning "within, inside, inner," from Greek ento-, comb. form of entos (adv., prep.) "within, inside," as a noun, "inner parts" (cognate with Latin intus), from PIE *entos, from *en "in" (see in) + adverbial suffix -tos, denoting origin.