Irish nationalist party (4,4)
I believe the answer is:
'irish nationalist party' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sinn fein that I've seen before include "Fine inns (anag.)" , "Irish political party" , "Political party to be found in fine inns" , "Gerry Adams's party" , "Irish political movement" .)