demeanor n.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

c. 1300, "declaration of hostile intent," also (early 14c.) "a threat or act of threatening," from Old French menace "menace, threat" (9c.), from Vulgar Latin minacia "threat, menace" (also source of Spanish amenaza, Italian minaccia), singular of Latin minaciæ "threatening things," from minax (genitive minacis) "threatening," from minari "threaten; jut, project," from minæ "threats; projecting points," from PIE root *men- (2) "to project." Applied to persons from 1936.