Assure (8)
'assure' is the definition.
(synonyms)
This is all the clue.
(Other definitions for convince that I've seen before include "Satisfy as to truth" , "Win over to your point of view" , "Be persuasive" , "Make believe" , "Persuade, satisfy" .)
'assure' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sew up that I've seen before include "Complete (something) satisfactorily" , "Polish off" , "Darn; conclude" , "Successfully complete" , "repair" .)