(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
a member of an ancient Jewish sect in Judea in the first century who fought to the death against the Romans and who killed or persecuted Jews who collaborated with the Romans