first lieu·ten·ant
noun/ˌfɜːst lefˈtenənt/
/ˌfɜːrst luːˈtenənt/
- an officer in the navy with responsibility for managing a ship, etc. under the guidance of the captain
舰务官 - an officer in the US army and air force just below the rank of a captain
（美国陆军和空军的）中尉 - (informal) a person who is the next most important to somebody
第二把手