Feline animal served up for rodent (6)
I believe the answer is:
marmot
'for rodent' is the definition.
(marmot is a kind of rodent)
'feline animal served up' is the wordplay.
'feline' becomes 'tom' (tom is a kind of feline).
'animal' becomes 'ram' (a male sheep).
'served up' says the letters should be written backwards (in a down clue, going upwards).
'tom'+'ram'='tomram'
'tomram' backwards is 'MARMOT'.
(Other definitions for marmot that I've seen before include "Large burrowing rodent" , "wild rodent" , "Furry burrowing rodent" , "Coarse-furred burrowing rodent" , "Stout, burrowing rodent" .)