Surly Republican in bunk … (5)
I believe the answer is:
gruff
'surly' is the definition.
(thesaurus)
'republican in bunk' is the wordplay.
'republican' becomes 'r' (abbreviation).
'in' means one lot of letters goes inside another.
'bunk' becomes 'guff' ('guff' can be a synonym of 'bunk').
'r' put inside 'guff' is 'GRUFF'.
(Other definitions for gruff that I've seen before include "Harsh - brusque" , "Abrupt in manner - rough and low in pitch" , "Sounding rough" , "Abrupt in sound or manner" , "Husky" .)