Cats in the pound (6)
I believe the answer is:
ounces
I believe this clue is a double definition.
'cats' is the first definition.
(I know this)
'in the pound' is the second definition.
(I've seen this before)
(Other definitions for ounces that I've seen before include "Small weights in UNESCO" , "They're equal to about 28 grams" , "Twelfths of a pound" , "Small units of weight" , "Undomesticated cats" .)