Guarantees certain bonds (8)
I believe the answer is:
sureties
'guarantees' is the definition.
(surety is a kind of guarantee)
'certain bonds' is the wordplay.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'bonds' becomes 'ties' (I've seen this in other clues).
'sure'+'ties'='SURETIES'
(Other definitions for sureties that I've seen before include "Assets that a creditor can claim from a defaulter" , "Guarantees for user site" .)