| Noun | 1. | atomistic theory - (chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles; "the ancient Greek philosophers Democritus and Epicurus held atomic theories of the universe" theory - a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory" chemical science, chemistry - the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions |