Contend with one brilliant in final check (8)
I believe the answer is:
militate
'contend' is the definition.
Both the definition and answer are verbs in their base form.
Perhaps they are linked in a way I don't understand?
'one brilliant in final check' is the wordplay.
'one' becomes 'i' (Roman numeral).
'brilliant' becomes 'lit' (brilliant can mean shining or lit up).
'in' means one lot of letters goes inside another.
'final check' becomes 'mate' (checkmate, the final check in a game of chess).
'i'+'lit'='ilit'
'ilit' inserted inside 'mate' is 'MILITATE'.
'with' is the link.
Can you help me to learn more?
(Other definitions for militate that I've seen before include "Have power (against)" , "Be a force (against)" , "Serve as strong influence against" , "Bring about an effect or change" , "Provide forceful evidence against" .)