Making good answer, interrupting old, irrational politician (9)

I believe the answer is:

expiatory

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'making good' is the definition.
Although both the answer and definition are adjectives, I can't see how one could define the other.

'answer interrupting old irrational politician' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'interrupting' indicates putting letters inside.
'old' becomes 'ex' (prefix meaning former or onetime).
'irrational' becomes 'pi' (an irrational number).
'politician' becomes 'tory' (term for a Conservative Party politician).
'ex'+'pi'+'tory'='expitory'
'a' going inside 'expitory' is 'EXPIATORY'.

Can you help me to learn more?

(Another definition for expiatory that I've seen is " Making atonement".)

I've seen this clue in The Times.

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