Declare Vera to be wrong (4)
I believe the answer is:
aver
'declare' is the definition.
(averring is a kind of declaring)
'vera to be wrong' is the wordplay.
'to be wrong' is an anagram indicator (I've seen 'is wrong' mean this).
'vera' with letters rearranged gives 'AVER'.
(Other definitions for aver that I've seen before include "Say firmly, rave if necessary" , "To declare or affirm solemnly as true" , "being assertive" , "Declare to be the case" , "Formally assert" .)