Wild cat returned and stole collie's stash (6)
I believe the answer is:
ocelot
'wild cat' is the definition.
(I've seen this before)
'returned and stole collie's stash' is the wordplay.
'returned' is a reversal indicator.
'stash' says the answer is hidden in the clue (I've seen 'stashes' mean this (I've seen this in other clues)).
'toleco' is hidden within 'and stole collies'.
'toleco' reversed gives 'OCELOT'.
(Other definitions for ocelot that I've seen before include "American wild cat" , "Wild cat, native to Central and South America - loo etc (anag)" , "Yellow-black striped and spotted cat" , "Big cat" , "Fur" .)