airman vs copilot

airman

• A pilot of an aircraft. 

• A naval seaman, especially one in the U.S. Navy, who works on and/or handles aircraft. 

• A member of an air force. 

• A person of a rank in the U.S. Air Force above airman basic and below airman first class. 

copilot

• A backup or assistant pilot of an aircraft. 

• To serve as relief or assistant pilot.