Claims one is argumentative (8)
I believe the answer is:
contends
'claims' is the definition.
(I know this)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for contends that I've seen before include "Fights or argues" , "Vies" , "Strives; maintains" , "Strives against another" , "Maintains or asserts" .)