Cat to come back, wanting bit of breakfast (5)
I believe the answer is:
ounce
'cat' is the definition.
(ounce can mean a snow leopard)
I cannot understand how the rest of the clue works.
(Other definitions for ounce that I've seen before include "Small amount (of old pound)" , "Approx. twenty-eight gm" , "Small quantity - weight" , "There are quite a few in the pound" , "Light weight coming in on cue" .)