Does it melt when the music's hot? (6)

I believe the answer is:

cornet

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'it melt when the music's hot?' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the remainder of the clue works.

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(Other definitions for cornet that I've seen before include "It's blown" , "Brass musical instrument" , "I could provide musical accompaniment" , "play this?" , "Brass instrument - ice cream" .)

I've seen this clue in the Evening Standard.

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