Crossword Genius

Sailor's flag at sea (4)

Ross

I believe the answer is:

jack

I believe this clue is a double definition.

'sailor's' is the first definition.
(informal term for a sailor)

'flag at sea' is the second definition.
(jack can mean a flag flown on a ship)

(Other definitions for jack that I've seen before include "Jill's companion" , "Man in navy" , "Lifting device - flag - boy's name - card - fish" , "Knave (cards)" , "Dog akin to 9" .)

I've seen this clue in The Guardian.
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