Grim end to a ship (5)
I believe the answer is:
stern
I believe this clue is a triple definition!
'grim' is the first definition.
(I know that grim can be written as stern)
'end' is the second definition.
(I have seen 'Rear end ' mean 'stern' so perhaps 'end' could also mean 'stern')
'to a' is a link.
'ship' is the third definition.
(thesaurus)
(Other definitions for stern that I've seen before include "Unsmiling" , "having a forbidding appearance" , "Poop" , "Rear; severe, serious" , "Severe part of the ship?" .)