occasionally psychodelic, 1956, of drugs, suggested by British-born Canadian psychiatrist Humphry Osmond (1917-2004) in a letter to Aldous Huxley and used by Osmond in a scientific paper published the next year; from Greek psykhe- "mind" (see psyche) + deloun "make visible, reveal," from delos "visible, clear," from PIE root *dyeu- "to shine" (see diurnal). In popular use from 1965 with reference to anything producing effects similar to that of a psychedelic drug or enhancing the effects of such a drug. As a noun from 1956.