/ drɒs; NAmE drɔːs; drɑːs/ noun [ U ]
1.
( especially BrE ) something of very low quality; the least valuable part of sth :
mass-produced dross
2.
( technical ) a waste substance, especially that separated from a metal when it is melted
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WORD ORIGIN
Old English drōs (in the sense scum on molten metal); related to Dutch droesem and German Drusen dregs, lees.