first officer

Noun

 * 1) The copilot of an aircraft.
 * 2) The chief mate of a merchant ship.
 * 3) The executive officer, second in command of a naval vessel.
 * 4) 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.
 * 5) Air Transport Auxiliary rank corresponding to Flight Lieutenant in the Royal Air Force.
 * 6) Women's Royal Naval Service rank corresponding to Lieutenant-Commander in the Royal Navy.