Mice, to cats (4)
I believe the answer is:
prey
'mice to cats' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for prey that I've seen before include "Quarry, fair game" , "Quarry, target" , "Animal hunted or caught for food" , "Victim, quarry" , "Hunted creature" .)