Commander, n.
Etymology: [Cf. F. commandeur. Cf. Commodore, Commender.]
1. A chief; one who has supreme authority; a leader; the chief officer of an army, or of any division of it. A leader and commander to the people. Is. lv. 4.
2. (Navy)
An officer who ranks next below a captain, -- ranking with a lieutenant colonel in the army.
3. The chief officer of a commandery.
2 more senses
4. A heavy beetle or wooden mallet, used in paving, in sail lofts, etc. Commander in chief, the military title of the officer who has supreme command of the land or naval forces or the united forces of a nation or state; a generalissimo. The President is commander in chief of the army and navy of the United States.
Syn. -- See Chief.
Shades of meaning
Fernald lists commander only as an antonym, under accessory.
He lists it without comment; the entries above explain its neighbors.