Sea swallow (4)
I believe the answer is:
tern
'sea swallow' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tern that I've seen before include "Rent out the bird" , "Pay rent for seabird" , "Rent out this gull" , "Winger" , "Gull-like sea bird" .)