- (military) The second lowest rank of a commissioned officer in the United States Army, Air Force, or Marine Corps, ranking above a second lieutenant and below a captain. The rank of first lieutenant is equivalent to the naval rank of lieutenant junior grade.
- (military) An equivalent rank in other military forces.
When used as a title, it is always capitalized.
- Example: First Lieutenant John Smith. The rank of first lieutenant corresponds to pay grade O-2.
Abbreviations: 1st Lieutenant, 1st Lt., 1st LT, and 1LT.
- lieutenant (abbreviation of "first lieutenant")
(highest lieutenant rank):