Carp, possibly, about popular conclusion (6)
I believe the answer is:
finish
'conclusion' is the definition.
(finish is a kind of conclusion)
'carp possibly about popular' is the wordplay.
'carp possibly' becomes 'fish' (carp is a kind of fish).
'about' indicates putting letters inside.
'popular' becomes 'in'.
'fish' going around 'in' is 'FINISH'.
(Other definitions for finish that I've seen before include "Conclude, wind up" , "Terminate, conclude" , "Put the final touches to" , "Treatment of surface" , "surface texture" .)