It's grim, getting set about by sailors! (5)
I believe the answer is:
stern
'it's grim' is the definition.
(synonyms)
'set about by sailors' is the wordplay.
'about' indicates anagramming the letters.
'by' says to put letters next to each other.
'sailors' becomes 'rn' (abbreviation for Royal Navy).
'set' anagrammed gives 'ste'.
'ste'+'rn'='STERN'
'getting' is the link.
(Other definitions for stern that I've seen before include "Demanding < back" , "Severe, demanding" , "Severe; grimly serious" , "Grim, strict" , "Grim; severe" .)