Rather small-minded Republican within (6)
I believe the answer is:
pretty
'rather' is the definition.
('pretty' can be a synonym of 'rather')
'small-minded republican within' is the wordplay.
'small-minded' becomes 'petty' ('petty' can be a synonym of 'small-minded').
'republican' becomes 'r' (abbreviation).
'within' indicates putting letters inside.
'petty' going around 'r' is 'PRETTY'.
(Other definitions for pretty that I've seen before include "Nice to look at" , "Delicately attractive" , "charming to look at" , "Fairly; appealing" , "Lovely" .)