Seabird's spin, say (4)
I believe the answer is:
tern
'seabird's' is the definition.
(tern is a kind of seabird)
'spin say' is the wordplay.
'spin' becomes 'turn' (I've seen this in another clue).
'say' shows a homophone (sound like).
'turn' sounds like 'TERN'.
(Other definitions for tern that I've seen before include "Sea bird, a small gull" , "Fork-tailed seabird" , "Fork-tailed relative of the gull" , "Gull-like sea bird" , "Small gull with forked tail" .)