Successful concern involves Republican, I see (8)
I believe the answer is:
thriving
'successful' is the definition.
(similar in meaning)
'concern involves republican i see' is the wordplay.
'concern' becomes 'thing' (thing is a kind of concern).
'involves' is an insertion indicator.
'republican' becomes 'r' (abbreviation).
'see' becomes 'v' (Latin 'vide', used to direct a reader to a source).
'r'+'i'+'v'='riv'
'thing' placed around 'riv' is 'THRIVING'.
(Other definitions for thriving that I've seen before include "having great success" , "Blooming" , "Affluent" , "Prospering" , "Prosperous" .)