(1):
(n.) A commissioned officer in the army, next below a captain.
(2):
(n.) A commissioned officer in the British navy, in rank next below a commander.
(3):
(n.) A commissioned officer in the United States navy, in rank next below a lieutenant commander.
(4):
(n.) An officer who supplies the place of a superior in his absence; a representative of, or substitute for, another in the performance of any duty.