Gull's relative (4)
I believe the answer is:
tern
'gull's relative' 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 "Fork-tailed seabird" , "Winger" , "Seagull" , "Gull-like sea bird" , "flier" .)