A selfish characteristic; no argument about it (6)
I believe the answer is:
agreed
'a selfish characteristic no' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'argument about it' is the wordplay.
I cannot really see how this works, but
'about' could be 're' ('re' means regarding or about) and 're' is located in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for agreed that I've seen before include "granted" , "Concurred - tallied" , "Acquiesed, concurred" , "Okayed" , "It's a deal!" .)