Animal seen in the menagerie (3)
I believe the answer is:
nag
'animal' is the definition.
(term for an old horse)
'in the menagerie' is the wordplay.
'in' indicates a hidden word.
'NAG' can be found hidden inside 'menagerie'.
'seen' is the link.
(Other definitions for nag that I've seen before include "Scold; inferior horse" , "Old Arab maybe" , "Worry constantly" , "shrew or > badger" , "Be persistently painful" .)