Where does the word “arrant” come from and What does it mean?

We use the word “arrant” now to mean downright, out-and-out, unmitigated; as, an arrant coward, an arrant scoundrel. But it was formerly just another spelling of “errant,” and it meant wandering, vagabond, nomad.

Thus a “knight errant,” in the Age of Chivalry, was a knight, usually young, who roamed the countryside, seeking an opportunity to win an accolade through good deeds.

In similar style a bandit or highwayman five or six centuries ago was termed an “arrant thief,” meaning one who wandered over the countryside, holding up persons whom he might encounter.