Horse and badger (3)
I believe the answer is:
nag
This clue is a double definition.
'horse' is the first definition.
(term for an old horse)
'badger' is the second definition.
(both can mean to annoy or complain at)
'and' is the link.
(Other definitions for nag that I've seen before include "Scold persistently, annoy" , "Badger with constant complaints" , "Scold like an old horse" , "Constantly scold - small horse" , "trouble constantly" .)