Proved to be false (8)
I believe the answer is:
rebutted
'proved to be false' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rebutted that I've seen before include "Refuted or disproved evidence or accusation" , "Overturned or disproved, say evidence" , "Proved to be false or incorrect" , "Refuted or disproved, say evidence" , "Opposed" .)