noun

• (uncountable) Lack of cleanliness.
  "They neither comb their Head, nor wash their Face, / But think their virtuous Nastiness a grace."
• (uncountable) Dirt, filth.
  "[T]he helliſh Noiſe, the Roaring, Svvearing, and Clamour, the Stench and Naſtineſs, and all the dreadful croud of Afflicting things that I ſavv there; joyn'd together to make the Place ſeem an Emblem of Hell itſelf, and a kind of an Entrance into it."
• (uncountable) Indecency; corruption; unkindness, meanness, spite, harshness, cruelty.
  "Among current novelists, Martin Amis lacks intellectual force but is well supplied with nastiness, which occasionally resembles humor."
• (uncountable) Unpleasantness, disagreeableness (to the senses).
  "Some medical beast had revived Tar-water in those days as a fine medicine, and Mrs. Joe always kept a supply of it in the cupboard; having a belief in its virtues correspondent to its nastiness."