Hound bank admitting blunder (7)
I believe the answer is:
terrier
'hound' is the definition.
(thesaurus)
'bank admitting blunder' is the wordplay.
'bank' becomes 'tier' (both can mean a row of similar things).
'admitting' indicates putting letters inside (admit can mean to welcome in or accept).
'blunder' becomes 'err' (to err is to make a mistake or blunder).
'tier' going around 'err' is 'TERRIER'.
(Other definitions for terrier that I've seen before include "Part-time soldier" , "Small, short-bodied dog" , "Dog - old land register" , "Persistent person" , "Dog bred for hunting" .)