Able to run in the heat (6)

I believe the answer is:

molten

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'able' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?

I don't understand how the rest of the clue works.

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(Other definitions for molten that I've seen before include "hot but ready to pour" , "State of moving lava" , "Reduced to liquid form by heating" , "Liquefied by heat" , "Liquid (of metal)" .)

I've seen this clue in the Evening Standard.

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