stain

To discolor, soil, or spot.

To bring into disrepute; taint or tarnish.

To change the color of (a piece of wood, for example) by applying a stain.

To treat (a specimen for the microscope) with a reagent or dye in order to identify cell or tissue structures or microorganisms.

To produce or receive discolorations.

A discolored or soiled spot or smudge.

A diminishment of one’s moral character or good reputation by being associated with something disgraceful.

A liquid substance applied especially to wood that penetrates the surface and imparts a rich color.

A reagent or dye used for staining microscopic specimens.

Specifically, a solution of a dye used in microscopical work to render more readily visible various structures, and for purposes of differentiation.