Brewer's: Aroint thee
Get ye gone, be off. In Cheshire they say, rynt ye, witch ; and milk-maids say to their cows when they have done milking them, rynt ye. (or 'roint) my beauties; but it is doubtful whether this is connected with the word in question.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894