Noun
1. a soiled or discolored appearance;
"the wine left a dark stain"2. (microscopy) a dye or other coloring material that is used in microscopy to make structures visible
3. the state of being covered with unclean things
4. a symbol of disgrace or infamy;
"And the Lord set a mark upon Cain"--Genesis5. an act that brings discredit to the person who does it;
"he made a huge blot on his copybook"