Dispute the honesty of (6)
I believe the answer is:
impugn
'dispute the honesty of' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for impugn that I've seen before include "Dispute the truth of" , "Call into question or attack by words" , "Express doubts about truth or honesty of, say motives" , "Try to discredit, express doubts about honesty" , "Attack verbally" .)