psy▫chol▫o▫gy (sī▫kol´ə▫jē) n. pl. ▫gies 1. The science of the human mind in any of its aspects, operations, powers, or functions. 2. The systematic investigation of mental phenomena, especially those associated with consciousness, behavior, and the problems of adjustment to the environment. 3. The aggregate of the emotions, traits, and behavior patterns regarded as characteristic of an individual, type, period, group, particular experience, etc.: the psychology of the fanatic; the psychology of love. 4. A work on psychology. Abbr. psych., psychol.