What is the meaning of Dross?

Waste or impure matter.

Residue that forms as a scum on the surface of molten metal from oxidation.

The impurities in metal.

A waste product from working with metal.

Worthless or trivial matter.

Residual raw opium left in an opium pipe which can be recycled for further sale or use.

To remove dross from.

brave, safe, sure; alternative form of drošs

Source: wiktionary.org