intrinsic (adj.)

late 15c., "interior, inward, internal," from Middle French intrinsèque "inner" (14c.), from Medieval Latin intrinsecus "interior, internal," from Latin intrinsecus (adv.) "inwardly, on the inside," from intra "within" (see intra-) + secus "along, alongside," from PIE *sekw-os- "following," suffixed form of root *sekw- (1) "to follow."

The form in English was conformed to words in -ic by 18c. Meaning "belonging to the nature of a thing" is from 1640s. Related: Intrinsical; intrinsically.