Bird or tool (12)
I believe the answer is:
yellowhammer
'bird' is the definition.
(yellowhammer is a kind of bird)
'or tool' is the wordplay.
'or' becomes 'yellow' ('or' is the heraldic name for gold or yellow).
'tool' becomes 'hammer' (hammer is a kind of tool).
'yellow'+'hammer'='YELLOWHAMMER'
(Other definitions for yellowhammer that I've seen before include "Sort of bunting" , "European bird - Orwell mayhem (anag)" , "Bird with the "a little bit of bread and no cheese" song" , "Type of bunting" , "Bird with a call supposed to sound like "a little bit of bread and no cheese"" .)