Definition of "psychedelic"

psychedelic

/ˈsaɪ.kəˌdɛl.ɪk/

adjective
comparative more psychedelic, superlative most psychedelic
1. Of, containing, generating, or reminiscent of drug-induced hallucinations, distortions of perception, altered awareness etc.
  Quotations
  With those drugs has come the psychedelic philosophy, an impassioned belief in the self-revealing, mind-expanding powers of potent weeds and seeds and chemical compounds known to man since prehistory but wholly alien to the rationale of Western society.
  1967, Joe David Brown, editor, The Hippies, New York: Time, Inc, page 2
2. (of graphics, etc.) Having bright colours, abstract shapes, etc. reminiscent of drug-induced hallucinations or distortions of perception.
noun
plural psychedelics
1. Any psychoactive substance (such as LSD or psilocybin) which, when consumed, causes perceptual changes (sometimes erratic and uncontrollable), visual hallucination, and altered awareness of the body and mind.
  Quotations
  I was going to become a three-drug connection to all my friends, psychedelics, hash and pot.
  2006, Dean McCormick, Dead End Street, page 62
interjection
1. (hippie slang) awesome, cool, groovy