Affirms positively (5)
I believe the answer is:
avers
'affirms positively' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for avers that I've seen before include "Alleges, asserts" , "States to be true" , "Declares to be true" , "Swears" , "States firmly - really raves" .)