Long-eared mammal (4)
I believe the answer is:
hare
'long-eared mammal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hare that I've seen before include "'You can't run with the . . . . and hunt with the hounds'" , "Leveret" , "may be electric!" , "Old saying: 'Let the .... sit" , "Fast runner" .)