by 1914 as "to subject to psychoanalysis," short for psychoanalyze. From 1934 as "to outsmart" (also psych out), and by 1952 in bridge as "make a bid meant to deceive an opponent." From 1963 as "to unnerve." However to psych (oneself) up is from 1972; to be psyched up "stimulate (oneself), prepare mentally for a special effort" is attested from 1968.
occasionally psychodelic, "producing expanded consciousness through heightened awareness and feeling," 1956, of drugs, suggested by British-born Canadian psychiatrist Humphry Osmond in a letter to Aldous Huxley and used by Osmond in a scientific paper published the next year; from Greek psykhē "mind" (see psyche) + dēloun "make visible, reveal" (from dēlos "visible, clear," from PIE root *dyeu- "to shine").
In popular use from 1965 with reference to anything producing effects or sensations similar to the common perception of the effects of a psychedelic drug. As a noun, "a psychedelic drug," from 1956.