Know how to use "fewer" and "less"? Find out.
word-forming element meaning "within, inside, on the inside," from Latin intra "on the inside, within," related to inter "between," from PIE *en-t(e)ro-, from root *en "in" (see in). Commonly opposed to extra-, but the use of intra as a prefix was rare in classical Latin.
A prefix meaning "inside" or "within," as in intravenous, within a vein.