Definitions of stain:

• noun:   a soiled or discolored appearance

  Example: "The wine left a dark stain"

• noun:   (microscopy) a dye or other coloring material that is used in microscopy to make structures visible
• noun:   a symbol of disgrace or infamy
• noun:   an act that brings discredit to the person who does it
• noun:   the state of being covered with unclean things
• verb:   color for microscopic study
• verb:   color with a liquid dye or tint

  Example: "Stain this table a beautiful walnut color"

• verb:   produce or leave stains

  Example: "Red wine stains the table cloth"

• verb:   make dirty or spotty, as by exposure to air; also used metaphorically
• name:  A surname (very rare: popularity rank in the U.S.: #36765)