: to conduct or behave (oneself) usually in a proper manner
… he might have been observed to demean himself as a person with nothing to do … Henry James †1916
Did you know?
There are two words spelled demean in English. The more familiar demean—"to lower in character, status, or reputation"—comes straight from mean, the adjective that means "spiteful." The other demean comes from the Anglo-French verb demener ("to conduct"), which in turn comes from Latin minare, meaning "to drive." This verb has been with us since the 14th century and is generally used in contexts (especially formal ones) specifying a type of behavior: "he demeaned himself in a most unfriendly manner"; "she demeaned herself as befitting her station in life"; "they knew not how to demean themselves in the king's presence." As you may have already guessed, the noun demeanor, meaning "behavior," comes from this demean.
Middle English demenen, demeynen "to rule, control, decide, arrange, keep within bounds, moderate, behave (in a certain way), conduct (oneself)," borrowed from Anglo-French demein-, tonic stem of demener "to lead, guide, carry on, subject to, treat, agitate," (intransitive) "to strive, thrash about," (reflexive) "to behave" (also continental Old & Middle French), from de-de- + mener "to lead, bring," going back to Latin mināre "to push, impel (an animal forward)," active form of the deponent verb minārī "to threaten" — more at minatory
Note: The verb mināre "to impel, drive (an animal)" is marginally attested in later classical Latin but more fully in Late Latin; in the Vulgate the object can also be human or inanimate. In early medieval Latin the notion "drive" shifted to "lead," a sense continued by Romance descendants of mināre (as French mener, Upper Engadine Romansh mner, Italian menare, Occitan & Catalan menar). The Old French prefixed derivative demener displays a wide array of meanings, which in part were passed through Anglo-French to Middle English demenen. The verbs in the modern languages—French démener, English demean—retain few of these meanings.