(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
serving to distinguish or identify a species or group; "the distinguishing mark of the species is its plumage"; "distinctive tribal tattoos"; "we were asked to describe any identifying marks or distinguishing features"
any personal belief about how to live or how to deal with a situation; "self-indulgence was his only philosophy"; "my father's philosophy of child-rearing was to let mother do it"
the rational investigation of questions about existence and knowledge and ethics
derived from experiment and observation rather than theory; "an empirical basis for an ethical theory"; "empirical laws"; "empirical data"; "an empirical treatment of a disease about which little is known"
(used informally especially for emphasis); "a real honest-to-god live cowboy"; "had us a high old time"; "went upriver to look at a sure-enough fish wheel"