Stain

noun
1.
a discoloration produced by foreign matter having penetrated into or chemically reacted with a material; a spot not easily removed.
2.
a natural spot or patch of color different from that of the basic color, as on the body of an animal.
3.
a cause of reproach; stigma; blemish:
a stain on one’s reputation.
4.
coloration produced by a dye that penetrates a substance, as wood.
5.
a dye made into a solution for coloring woods, textiles, etc.
6.
a reagent or dye used in treating a specimen for microscopic examination.
verb (used with object)
7.
to discolor with spots or streaks of foreign matter.
8.
to bring reproach or dishonor upon; blemish.
9.
to sully with guilt or infamy; corrupt.
10.
to color or dye (wood, cloth, etc.) by any of various processes that change or react with the substance chemically.
11.
to color with something that penetrates the substance.
12.
to treat (a microscopic specimen) with some reagent or dye in order to color the whole or parts and so give distinctness, contrast of tissues, etc.
verb (used without object)
13.
to produce a stain.
14.
to become stained; take a stain:
This fabric stains easily.
verb (mainly transitive)
1.
to mark or discolour with patches of something that dirties: the dress was stained with coffee
2.
to dye with a penetrating dyestuff or pigment
3.
to bring disgrace or shame on: to stain someone’s honour
4.
to colour (specimens) for microscopic study by treatment with a dye or similar reagent
5.
(intransitive) to produce indelible marks or discoloration: does ink stain?
noun
6.
a spot, mark, or discoloration
7.
a moral taint; blemish or slur
8.
a dye or similar reagent, used to colour specimens for microscopic study
9.
a solution or liquid used to penetrate the surface of a material, esp wood, and impart a rich colour without covering up the surface or grain
10.
any dye that is made into a solution and used to colour textiles and hides

stain (stān)
n.

A reagent or dye that is used for staining microscopic specimens.

A procedure in which a dye or a combination of dyes and reagents is used to color the constituents of cells and tissues.

v. stained, stain·ing, stains
To treat specimens for the microscope with a reagent or dye that makes visible certain structures without affecting others.