demeanour: [15] A person’s demeanour is how they ‘conduct’ themselves. The word goes back ultimately to the literal notion of driving animals along. It is a derivative of the now virtually obsolete reflexive verb demean ‘behave’, borrowed in the 13th century from Old French demener. This was a compound formed from the intensive prefix de- and mener ‘lead’, a descendant of Latin mināre ‘drive a herd of animals’ (whose original connotation of ‘urging on with threats’ is revealed by its close relationship with minārī ‘threaten’, source of English menace).
This obsolete demean should not, incidentally, be confused with demean ‘degrade’ [17], which was formed from the adjective mean. => menace[demeanour etymology, demeanour origin, 英语词源]