Rabbit or donkey (2,2)
I believe the answer is:
go on
'rabbit' is the definition.
(rabbit can mean to go on and on)
I can't explain the rest of the clue.
(Other definitions for go on that I've seen before include "Witter - words of encouragement" , "Stupid person or ruffian - go on with it" , "Foolish person - thug (US)" , "Silly person - bully (US)" , "eg Spike Milligan" .)