An acknowledgement of minor explosion? (5,3)

I believe the answer is:

thank you

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'an acknowledgement' is the definition.
(thank you is a kind of acknowledgement)

I can't explain the rest of the clue.

(Other definitions for thank you that I've seen before include "Much obliged!" , "I'm grateful" , "Polite reply (to gift)" , "Words of acknowledgement" , "Conventional expression of gratitude" .)

I've seen this clue in The Telegraph.

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