Bird's extremely sharp weapon (7)
I believe the answer is:
sparrow
'bird's' is the definition.
(sparrow is a kind of bird)
'extremely sharp weapon' is the wordplay.
'extremely' suggests removing the centre.
'weapon' becomes 'arrow' (arrow is a kind of weapon).
'sharp' with its centre taken out is 'sp'.
'sp'+'arrow'='SPARROW'
(Other definitions for sparrow that I've seen before include "one on the wing" , "House bird" , "A chirrupy city bird" , "Pirate" , "Little brown bird" .)