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adj. nas·ti·er, nas·ti·est
a. Disgusting or repellent: a nasty odor rising from the garbage can. See Synonyms at offensive.
b. Unpleasantly cold or wet: nasty weather.
c. Archaic Dirty; filthy.
2. Morally offensive or indecent: a nasty film.
a. Unpleasant or annoying: a nasty habit.
b. Mean or spiteful: Stop being nasty to each other.
4. Painful or dangerous; grave: a nasty accident.
5. Exasperatingly difficult to solve or handle: a nasty puzzle; a nasty problem.
n. pl. nas·ties
One that is nasty: "It is the business of museums to present us with nasties as well as with fine things" (Country Life).
[Middle English nasti, filthy, possibly alteration of Old French nastre, bad, short for villenastre : vilein, bad; see villain + -astre, pejorative suff. (from Latin -aster).]