'behaviorism' originates from English, formed in the early 20th century from the noun 'behavior' with the suffix '-ism' (denoting a doctrine or system).

'behavior' came from Middle English 'behaviour', itself from the verb 'behave' (be- + 'have' meaning 'to have, hold'); 'behaviour' developed into modern English 'behavior', and the suffix '-ism' was later attached to create 'behaviorism' as the name of a theoretical doctrine.

Initially, 'behavior' meant 'the manner of behaving' or 'one's conduct'; over time 'behaviorism' came to mean specifically the psychological school that explains behavior in terms of observable stimulus–response processes rather than introspection or inner mental states.