Mien, n.
Etymology: [F. mine; perh. from sane source as mener to lead; cf. E. demean, menace, mine, n.]
Aspect; air; manner; demeanor; carriage; bearing. Vice is a monster of so frightful mien, As, to be hated, needs but to be seen. Pope.
Shades of meaning
Fernald has no entry of its own for mien; he lists it under air.
Where he writes about it:
Mien is closely synonymous with air, but less often used in a bad sense. — from air
We say a rakish air rather than a rakish mien. — from air
Mien may be used to express some prevailing feeling; as, "an indignant mien." Demeanor goes beyond appearance, including conduct, behavior; as, a modest demeanor. — from air