End concealed in genuine refutation (8)
I believe the answer is:
rebuttal
'refutation' is the definition.
(I know that rebuttal is a type of refutation)
'end concealed in genuine' is the wordplay.
'end' becomes 'butt' (I've seen this before).
'concealed in' means one lot of letters goes inside another.
'genuine' becomes 'real' (similar in meaning).
'butt' inserted inside 'real' is 'REBUTTAL'.
(Other definitions for rebuttal that I've seen before include "counterclaim" , "Counter-statement" , "A contradiction of evidence" , "Negation" , "Disproof" .)