Others endlessly mull over; I have an answer (9)

I believe the answer is:

responder

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'i have an answer' is the definition.
I can't tell whether this defines the answer.

'others endlessly mull' is the wordplay.
'others' becomes 'rest' (eg the rest of a group).
'endlessly' means to remove the last letter.
'mull' becomes 'ponder' (synonyms).
'rest' with its last letter removed is 'res'.
'res'+'ponder'='RESPONDER'

'over' acts as a link.

Can you help me to learn more?

(Other definitions for responder that I've seen before include "provides one with the answer" , "One replying or reacting" , "one should give a reply" , "Reactor" , "one giving a reaction" .)

I've seen this clue in The Guardian.

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