Surly Republican cutting through nonsense (5)
I believe the answer is:
gruff
'surly' is the definition.
(I've seen this in another clue)
'republican cutting through nonsense' is the wordplay.
'republican' becomes 'r' (abbreviation).
'cutting through' indicates putting letters inside.
'nonsense' becomes 'guff' (I've seen this before).
'r' put into 'guff' is 'GRUFF'.
(Other definitions for gruff that I've seen before include "Rasping - ungracious" , "Curt and surly" , "(Of voice) rough, low" , "Sounding rough" , "Harsh - brusque" .)