A blackbird (4)
I believe the answer is:
crow
'a blackbird' is the definition.
(crow blackbird is a kind of blackbird)
This is all the clue.
(Other definitions for crow that I've seen before include "Make sounds of pleasure as a baby does - or a bird" , "One joins others in a murder" , "Black bird; boast" , "Black bird; brag" , "One commonly stoned" .)