Firm very popular round Republican group (6)
I believe the answer is:
cohort
'group' is the definition.
The answer is an example.
'firm very popular round republican' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'very popular' becomes 'hot' (I've seen this in another clue).
'round' means one lot of letters goes inside another.
'republican' becomes 'R' (political abbreviation).
'hot' enclosing 'r' is 'hort'.
'co'+'hort'='COHORT'
(Other definitions for cohort that I've seen before include "Ancient Roman military unit" , "Band of warriors" , "Group with a shared characteristic - unit of Roman legion" , "Fighting band; part of Roman legion" , "Unit of Roman soldiers - group of people of same age" .)