Sentence:  <WSD>Eraser dust</WSD>, a commercially manufactured fine, eraser residue, often is used by draftspersons to keep the drawing free from the inevitable smudges caused when triangles and T squares pick up minute amounts of lead residue and spread it onto other parts of the surface. 
Meaning of the word marked with <WSD> tags:  A finely powdered plastic that is used to clean smudges from pencil drawings.