In Macbeth, Act I, Scene III, we find ourselves once again on the heath with the Three Witches, where the following dialogue takes place:

 FIRST WITCH. Where hast thou been, sister?
  SECOND WITCH. Killing swine.
  THIRD WITCH. Sister, where thou?
  FIRST WITCH. A sailor's wife had chestnuts in her lap,
  And mounch'd, and mounch'd, and mounch'd. "Give me,"quoth I.
    "Aroint thee, witch!" the rump-fed ronyon cries.
    Her husband's to Aleppo gone, master the Tiger;
    But in a sieve I'll thither sail,
    And, like a rat without a tail,
    I'll do, I'll do, and I'll do. (Macbeth I:III)

It seems the First Witch had come across a Sailor's Wife, who is clearly accustomed to luxury. The Wife is 'rump-fed,' meaning she has the well-fed appearance of a a person who apparently eats very choice cuts of meat and is probably luxuriously fat as a result; the First Witch also describes this woman as a ronyon--a scab. The Wife is eating chestnuts and when the First Witch asks for them, the Wife cries, "Aroint thee, witch!"--meaning "Begone!"

The term "aroint" is of uncertain origin. Swan Macbeth notes that it is found in Macbeth, in King Lear, and in no other sources. It is speculated that Shakespeare derived 'aroint thee' from an expression in the local dialect of Cheshire, that may have been said to cattle to settle them when they were restless, as though bewitched.

The First Witch decides to curse the sailor because his wife has insulted her, and dismissed her very rudely. Because of his wife's rudeness, the First Witch decides to pursue the sailor in his ship, the Tiger, to Aleppo, a mysterious and far-distant port in Syria. There, like a rat, the Witch intends to gnaw holes in his ship so that he will be lost at sea.