"1956, of drugs, suggested by H. Osmond in a letter to Aldous Huxley and used by Osmond in a scientific paper published the next year; from Gk. psykhe- "mind" + deloun "make visible, reveal," " Psychedelia is from 1967."

Source:
http://www.etymonline.com/index.php

"The word psychedelic is an English term coined from the Greek words for "mind," ψυχή (psyche), and "manifest," δήλος (delos). A psychedelic experience is characterized by the perception of aspects of one's mind previously unknown, or by the creative exuberance of the mind liberated from its ostensibly ordinary fetters. Psychedelic states are an array of experiences elicited by sensory deprivation as well as by psychedelic substances. Such experiences include hallucinations, changes of perception, synesthesia, altered states of awareness, mystical states, and occasionally states resembling psychosis.

The term was first coined as a noun in 1957 by psychiatrist Humphry Osmond as an alternative descriptor for hallucinogenic drugs in the context of psychedelic psychotherapy. The term featured prominently in a now-famous exchange with Aldous Huxley, in which the little-used term phanerothyme (derived from roots relating to "spirit" or "soul") was suggested:

To make this trivial world sublime,
take half a gram of phanerothyme.
Osmond responded:

To fathom Hell or soar angelic,
just take a pinch of psychedelic.
Timothy Leary, who was largely responsible for the popularization of the term "psychedelic",[citat ion needed] was a well-known proponent of their use, as was Aldous Huxley. Both, however, advanced widely different opinions on the broad use of psychedelics by state and civil society. Leary promulgated the idea of such substances as a panacea, while Huxley suggested that only the cultural and intellectual elite should partake of entheogens systematically.

The use of psychedelic drugs became widespread in the modern West in the mid-1960s. One of the first uses of the word in the music scene of this time was in the 1964 recording of "Hesitation Blues" by the Holy Modal Rounders. The term was introduced to rock music and popularized by the 13th Floor Elevators 1966 album The Psychedelic Sounds of the 13th Floor Elevators."
Source and further information:
http://en.wikipedia.org/wiki/Psychedelic

haha. I just used this word to describe the colour orange...how interesting. :P

nigga please?