Psychedelic  adj. 1 a expanding the mind's awareness etc., esp. With hallucinogenic drugs. B hallucinatory; bizarre. C (of a drug) producing hallucinations. 2 colloq. A producing a hallucinatory effect; vivid in colour or design etc. B (of colours, patterns, etc.) Bright, bold, and often abstract. [greek psukhe mind, delos clear]