Brief confusion concluded, made a chum (10)
I believe the answer is:
befriended
'made a chum' is the definition.
The answer and definition can be both to do with social activities as well as being past participle verbs.
Perhaps there's an association between them I don't understand?
'brief confusion concluded' is the wordplay.
'confusion' indicates anagramming the letters.
'concluded' becomes 'ended' (synonyms).
'brief' anagrammed gives 'befri'.
'befri'+'ended'='BEFRIENDED'
Can you help me to learn more?
(Other definitions for befriended that I've seen before include "assisted?" , "Treated as ally" , "Became mates with (someone)" .)