"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."
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.
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Definitions of behaviorism from WordNet
an approach to psychology that emphasizes observable measurable behavior;