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.
An equivalent rank in other military forces.
Women's Royal Naval Service rank corresponding to Lieutenant-Commander in the Royal Navy.
Air Transport Auxiliary rank corresponding to Flight Lieutenant in the Royal Air Force.
The copilot of an aircraft.
The chief mate of a merchant ship.
The executive officer, second in command of a naval vessel.
The most senior civil servant in the United States Foreign Service, with responsibility for running an embassy under the authority of and reporting to the ambassador.