Rejection of a request (6)
I believe the answer is:
denial
'rejection of a request' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for denial that I've seen before include "Saying it isn't so" , "Rejection of a request" , "Nailed (anag.)" , "Refusal to accept an unpalatable truth" , "Rejection or refusal" .)