Demeanor

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late 15th century: from demean2, probably influenced by obsolete havour ‘behaviour’.

wiktionary

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From Middle English demenen, demeinen, from Anglo-Norman demener, from Old French demener, from de- + mener(“to conduct, lead”) + -or, from Latin *mināre(“to drive”) and Latin minārī(“to project or jut forth”).

etymonline

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demeanor (n.)

late 15c., demenure, "conduct, management, treatment, behavior toward someone," from obsolete Middle English demean, demeinen "to handle, manage, conduct," later "behave in a certain way, conduct oneself" (early 14c.), from Old French demener (11c.) "to guide, conduct; to live, dwell," from de- "completely" (see de-) + mener "to lead, direct," from Latin minari "to threaten," in Late Latin "to drive (a herd of animals);" see menace (n.). Meaning "behavior, bearing, deportment" is from late 15c. Spelling changed by influence of nouns in -or, -our.