Serving as correction, speed of light accelerating (10)

I believe the answer is:

chastening

'serving as correction' is the definition.
(to chasten is to correct or punish)

'speed of light accelerating' is the wordplay.
'speed of light' becomes 'c' (as in E=mc2).
'accelerating' becomes 'hastening' (to hasten is to speed up).
'c'+'hastening'='CHASTENING'

I've seen this clue in The Guardian.

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