Sailor in boat arriving (3)
I believe the answer is:
tar
'sailor' is the definition.
(slang term for a sailor)
'in boat arriving' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TAR' is hidden within 'boat arriving'.
(Other definitions for tar that I've seen before include "Sticky stuff for a kind of sailor" , "Black viscid substance" , "Dark flammable liquid" , "Harmful tobacco residue" , "Flammable liquid; sailor" .)