word-forming element meaning "within, inside, on the inside," from Latin preposition intra "on the inside, within, in, into;" of time, "during, in the course of," related to inter "between," from PIE *en-t(e)ro-, from root *en "in." Commonly opposed to extra-, and compare inter-. The use of intra as a prefix was rare in classical Latin.
1872, "of or pertaining to the human soul" (earlier psychical, 1640s), from Greek psykhikos "of the soul, spirit, or mind" (opposed to somatikos), also (New Testament) "concerned with the life only, animal, natural," from psykhē "soul, mind, life" (see psyche).
The meaning "characterized by psychic gifts; pertaining to the class of extraordinary and obscure phenomena of the mind not usually treated by psychologists" (mind-reading, second sight, etc.) is attested from 1871.