Bird's down (7)
I believe the answer is:
swallow
I believe this is a double definition.
'bird's' is the first definition.
(swallow is a kind of bird)
'down' is the second definition.
(thesaurus)
(Other definitions for swallow that I've seen before include "Eat or drink" , "One of these does not make a spring" , "flier" , "One doesn't make a summer, they say" , "Songbird" .)