Behavior

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late Middle English: from behave, on the pattern of demeanour, and influenced by obsolete haviour from have.

wiktionary

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From Middle English behavoure, behaver, equivalent to behave +‎ -ior, apparently in imitation of English havior, haviour, havour. Compare Scots havings(“behavior”), from have(“to behave”).

etymonline

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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."