The Collaborative International Dictionary of English v.0.48:
Nasty \Nas"ty\ (n[.a]s"t[y^]), a. [Compar. Nastier
(n[.a]s"t[i^]*[~e]r); superl. Nastiest.] [For older nasky;
cf. dial. Sw. naskug, nasket.]
1. Offensively filthy; very dirty, foul, or defiled;
2. Hence, loosely: Offensive; disagreeable; unpropitious;
wet; drizzling; as, a nasty rain, day, sky.
3. Characterized by obscenity; indecent; indelicate; gross;
4. Vicious; offensively ill-tempered; insultingly mean;
spiteful; as, a nasty disposition.
5. Difficult to deal with; troublesome; as, he fell of his
bike and got a nasty bruise on his knee. [slang]
Syn: Nasty, Filthy, Foul, Dirty.
Usage: Anything nasty is usually wet or damp as well as
filthy or dirty, and disgusts by its stickiness or
odor; but filthy and foul imply that a thing is filled
or covered with offensive matter, while dirty
describes it as defiled or sullied with dirt of any
kind; as, filthy clothing, foul vapors, etc.