Refusal to do business around N. Ireland (6)
I believe the answer is:
denial
'refusal' is the definition.
(I've seen this in another clue)
'do business around n ireland' is the wordplay.
'do business' becomes 'deal' (as in dealing with another business).
'around' means one lot of letters goes inside another.
'n ireland' becomes 'NI' (Northern Ireland).
'deal' enclosing 'ni' is 'DENIAL'.
'to' acts as a link.
(Other definitions for denial that I've seen before include "Refusal to acknowledge" , "Rejection of a request" , "Repudiation" , "Act of asserting that something alleged is not true" , "Refusal to accept an unpalatable truth" .)