Coining the word
It combines the Greek psyché, "mind" or "soul," with dēlos, "visible" or "clear," and the related verb dēloun, "to reveal" or "make manifest" — together suggesting something that reveals the mind or soul.
The British psychologist Humphry Osmond wrote to the author Aldous Huxley in 1957 in search of a word for this class of substances. Huxley proposed "phanerothyme," combining Greek roots for "manifest" and "spirit," and offered it in verse. Osmond replied with his own coinage in a matching couplet — "To fathom Hell or soar angelic / Just take a pinch of psychedelic" — and it was his word, not Huxley's, that stuck.