Pronunciation: (at'u-miz"um), [key]
1. Also called atomic theory. Philos.the theory that minute, discrete, finite, and indivisible elements are the ultimate constituents of all matter.
2. Psychol.a method or theory that reduces all psychological phenomena to simple elements.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.