stain

a soiled or discolored appearance; "the wine left a dark stain"

(microscopy) a dye or other coloring material that is used in microscopy to make structures visible

the state of being covered with unclean things

a symbol of disgrace or infamy; "And the Lord set a mark upon Cain"--Genesis

an act that brings discredit to the person who does it; "he made a huge blot on his copybook"

color with a liquid dye or tint; "Stain this table a beautiful walnut color"; "people knew how to stain glass a beautiful blue in the middle ages"

produce or leave stains; "Red wine stains the table cloth"

make dirty or spotty, as by exposure to air; also used metaphorically; "The silver was tarnished by the long exposure to the air"; "Her reputation was sullied after the affair with a married man"

color for microscopic study; "The laboratory worker dyed the specimen"