Gull's kin (4)
I believe the answer is:
tern
'gull's kin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tern that I've seen before include "Seagull" , "Rent out this gull" , "Rent out the bird" , "Gull-like seabird" , "Three-masted schooner" .)