(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"
(psychology) a theory that reduces all mental phenomena to simple elements (sensations and feelings) that form complex ideas by association
(law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature); "the rationale for capital punishment"; "the principles of internal-combustion engines"
confidently aggressive; "too assertive as a salesman"; "his self-assertive and unflagging energy"
inclined to bold and confident assertion; aggressively self-assured; "an energetic assertive boy who was always ready to argue"; "pointing directly at a listener is an assertive act"
marked by excessive confidence; "an arrogant and cocksure materialist"; "so overconfident and impudent as to speak to the queen"; "the less he knows the more positive he gets"
tending to bring about; being partly responsible for; "working conditions are not conducive to productivity"; "the seaport was a contributing factor in the growth of the city"; "a contributory factor"