occasionally psychodelic, 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 similar to that of a psychedelic drug or enhancing the effects of such a drug. As a noun from 1956.
