Mammal or bird (6)
I believe the answer is:
animal
'mammal or bird' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for animal that I've seen before include "Such as 13 ac" , "Kind of instinct" , "Animate being" , "It shares the world with vegetable and mineral" , "Brutal, sensual" .)