Certificate (7)
'certificate' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for voucher that I've seen before include "Something that can be exchanged for goods or services" , "Coupon; receipt" , "Document that can be exchanged for goods" , "Paper token" , "Document that serves as evidence of some expenditure" .)
'certificate' is the definition.
(academic certificate)
This is all the clue.
(Other definitions for diploma that I've seen before include "official document" , "Academic award" , "Certificate awarded by college for educational attainment" , "Certificate of competency" , "Document conferring a qualification" .)
'certificate' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for licence that I've seen before include "Legal document giving official permission" , "Authority (or the lack of it!)" , "Grant of permission" , "A writer's exaggeration" , "Official autorisation" .)