Genuine about target for refutation (8)
I believe the answer is:
rebuttal
'for refutation' is the definition.
(rebuttal is a kind of refutation)
'genuine about target' is the wordplay.
'genuine' becomes 'real' (similar in meaning).
'about' means one lot of letters goes inside another.
'target' becomes 'butt' (synonyms).
'real' going around 'butt' is 'REBUTTAL'.
(Other definitions for rebuttal that I've seen before include "Counter-argument" , "reply to accusation" , "arguing to the contrary" , "A contradiction of evidence" , "Negation" .)