A black bird (4)
I believe the answer is:
crow
'a black bird' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for crow that I've seen before include "Brag; carrion bird" , "Make sounds of pleasure as a baby does - or a bird" , "Black bird; boast" , "Ugly old woman" , "One joins others in a murder" .)