Allege as fact (4)
I believe the answer is:
aver
'allege as fact' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aver that I've seen before include "Firmly maintain" , "Declare to be the case" , "Maintain - assert - allege" , "'Affirm, assert (4)'" , "Declare or insist" .)