Word Origin & History
nastyc.1400, "foul, filthy, dirty, unclean," perhaps from O.Fr. nastre "bad, strange," shortened form of villenastre "infamous, bad," from vilein "villain" + -astre, pejorative suffix, from L. -aster. Alternative etymology is from Du. nestig "dirty," lit. "like a bird's nest." Likely reinforced by a Scand.
source (cf. Swed. dial. naskug "dirty, nasty"). Of weather, from 1634; of things generally, "unpleasant, offensive," from 1705. Of people, "ill-tempered," from 1825.