Northern Ireland in trade rebuttal (6)
I believe the answer is:
denial
'rebuttal' is the definition.
(I've seen this in another clue)
'northern ireland in trade' is the wordplay.
'northern ireland' becomes 'NI' (abbreviation).
'in' is an insertion indicator.
'trade' becomes 'deal' (synonyms).
'ni' going inside 'deal' is 'DENIAL'.
(Other definitions for denial that I've seen before include "Declaration that something is untrue" , "Refusal to accept an unpalatable truth" , "Nailed (anag.)" , "Daniel (anag.)" , "Repudiation" .)