1. A deputy of or substitute for another; one acting by vicarious authority (he sent his chief lieutenant to the meeting).
2. A composite part of the title of many government and military officials who are subordinate to others, esp. when the duties of the higher official may devolve to the subordinate (lieutenant governor).
3. In the U.S. Army, a commissioned officer next below captain.
4. In the U.S. Navy, an officer next below lieutenant commander.
