Merriam-Webster Collegiate Dictionary - psychedelic

 I. noun  Etymology: irregular from psych- + Greek deloun to show, from delos evident; akin to Sanskrit dideti it shines, Latin dies day — more at deity  Date: 1956 a ~ drug (as LSD)  II. adjective  Date: 1957  1.  a. of, relating to, or being drugs (as LSD) capable of producing abnormal psychic effects (as hallucinations) and sometimes psychotic states  b. produced by or associated with the use of ~ drugs a ~ experience  2. imitating, suggestive of, or reproducing effects (as distorted or bizarre images or sounds) resembling those produced by ~ drugs ~ color schemes  • ~ally adverb