/ Dictionary / Index P psychoactive: Meaning and Definition of Find definitions for: psy•cho•ac•tive Pronunciation: (sī"kō-ak'tiv), [key] — adj. of or pertaining to a substance having a profound or significant effect on mental processes: a psychoactive drug. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: psychoactive (Thesaurus) psychoacoustics psychoanal. Related Content Daily Word Quiz: mongrel Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language