Collective punishment? Certainly not (8)

I believe the answer is:

solitary

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'collective punishment?' is the definition.
'solitary' can be an answer for 'punishment?' (I've seen this before). I am not certain of the 'collective' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for solitary that I've seen before include "Left alone" , "'Sole, lone (8)'" , "Lone; isolated" , "Recluse" , "punishment" .)

I've seen this clue in The Times.

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