1.NounSomeone whose occupation is operating a ship or boat at sea, for either civilian or military purposes.
"An intergovernmental panel will draw up plans to relieve seafarers who have been stuck at sea during a crisis."
2.NounAnyone who travels by sea.
"Clearly the earliest Australians were seafarers who landed there tens of thousands of years ago; our quest to know more about them — did they come from Melanesia? what kind of boats did they have? were they blown out to sea by a storm? — is ongoing."