Worthless matter (5)

I believe the answer is:

dross

'worthless matter' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for dross that I've seen before include "Rubbish, scum" , "Rubbish; impurities" , "Refuse - dregs" , "Impurity" , "Worthless matter" .)

I've seen this clue in The Independent.

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