WordNet sense 1 (the state of being covered with unclean things):

dirt, filth, grease, grime, grunge, soil

WordNet sense 2 (a symbol of disgrace or infamy):

brand, mark, stigma

WordNet sense 3 (a soiled or discolored appearance):

discoloration, discolouration

WordNet sense 4 (make dirty or spotty, as by exposure to air; also used metaphorically):

defile, sully, tarnish, maculate, defile

WordNet sense 5 (an act that brings discredit to the person who does it):

blot, smear, smirch, spot