"theory that human and animal behavior can be explained in terms of conditioning," 1913, coined by U.S. psychologist John B. Watson (1878-1958) from behavior + -ism. Behaviorist is from the same time.
Entries linking to behaviorism
behavior n.
"manner of behaving (whether good or bad), conduct, manners," late 15c., essentially from behave, but with ending from Middle English havour "possession," a word altered (by influence of have) from aver, noun use of Old French verb aveir "to have."
-ism
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.