Vouch (6)
'vouch' is the definition.
(I know that vouch is a kind of attest)
This is the entire clue.
(Other definitions for attest that I've seen before include "Corroborate" , "Demonstrate" , "Certify or bear witness" , "Provide proof of, declare to be true (6)" , "Give testimony in a court of law" .)
'vouch' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for aver that I've seen before include "State firmly, maybe rave" , "Prove to be true" , "Say firmly, rave if necessary" , "Firmly maintain" , "State firmly, declare" .)