Chemical compound by reactor had decayed (12)

I believe the answer is:

carbohydrate

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'chemical' is the definition.
(thesaurus)

'compound by reactor had decayed' is the wordplay.
'by reactor had' anagrams to 'CARBOHYDRATE'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

(Another definition for carbohydrate that I've seen is " Type of food".)

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