Merriam-Webster's Collegiate® Dictionary, 11th Edition
DIRTY
I. adjective (dirtier; -est)
Date: 14th century
1. not clean or pure , likely to befoul or defile with dirt , contaminated with infecting organisms , containing impurities ,
2. morally unclean or corrupt: as, indecent , vulgar , dishonorable , base , unsportsmanlike , acquired by disreputable or illegal means ; ill-gotten , disagreeable, distasteful, or objectionable but usually necessary (as in achieving a desired result) ,
3. abominable , hateful , highly regrettable , likely to cause disgrace or scandal , foggy , stormy ,
5. not clear and bright ; dullish , characterized by a husky, rasping, or raw tonal quality , conveying ill-natured resentment , having considerable fallout , dirtily adverb dirtiness noun Synonyms: see: dirty
II. adverb (dirtier; -est)
Date: circa 1931
in a dirty manner: as, deceptively, underhandedly , indecently ,
III. verb (dirtied; dirtying)
Date: 1591
transitive verb to make dirty,
2. to stain with dishonor ; sully , to debase by distorting the real nature of, intransitive verb to become soiled