Republican's opponent, single-minded type full of cunning (10)
I believe the answer is:
monarchist
'republican's opponent' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'single-minded type full of cunning' is the wordplay.
'single minded type' becomes 'monist' (I can't justify this - if you can you should believe this answer much more).
'full of' means one lot of letters goes inside another.
'cunning' becomes 'arch' (arch can mean cunning or tricksy).
'monist' placed around 'arch' is 'MONARCHIST'.
Can you help me to learn more?
(Other definitions for monarchist that I've seen before include "Royal supporter" , "Supporter of hereditary rule" .)