Slow reply to cyanide dealer, perhaps (7,8)

I believe the answer is:

delayed reaction

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'slow reply to cyanide dealer perhaps' is the definition.
I can't tell whether this defines the answer.

'slow reply to cyanide dealer perhaps' is the wordplay.
'to cyanide dealer' can be anagrammed to 'DELAYED REACTION'.
However, I'm not clear how this is indicated.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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