When refined, is it dearest? (5)

I believe the answer is:

sugar

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'dearest?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for sugar that I've seen before include "rotter!" , "White or brown sweetener" , "Damn" , "Common sweetener" , "for such a daddy" .)

I've seen this clue in the Evening Standard.

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