Once beaten, explained everything (9)

I believe the answer is:

expounded

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'explained everything' is the definition.
I can't judge whether this definition defines the answer.

'once beaten' is the wordplay.
'once' becomes 'ex' (prefix meaning former or onetime).
'beaten' becomes 'pounded' ('pound' can be a synonym of 'beat').
'ex'+'pounded'='EXPOUNDED'

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(Other definitions for expounded that I've seen before include "made clear" , "Explained" , "commented on" .)

I've seen this clue in The Globe and Mail.

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