transitive verb

1. to spoil the appearance of by patches or streaks of color or dirt; discolor; spot
2. to bring shame upon (someone's character, reputation, etc.); taint; disgrace; dishonor
3. to change the appearance of (wood, glass, etc.) by applying a dye, pigment, etc.
4. to treat (material for microscopic study) with a coloring matter that facilitates study, as by making transparent parts visible or by producing a different effect upon different structures or tissues

Etymology: ME stainen, aphetic < disteinen, distain: sense and form infl. by ON steinn, color, lit., stone (hence, mineral pigment)

intransitive verb

noun

1. a discoloration, streak, or spot resulting from staining
2. a moral blemish; dishonor; guilt; taint a stain on one's reputation
3. a substance used to impart color in staining; specif.,
   1. a dye or pigment in solution, esp. one that penetrates a wood surface
   2. a dye used to stain material for microscopic study