A knight-errant[1] (or knight errant[2]) is a figure of medieval chivalric romance literature. The adjective errant (meaning "wandering, roving") indicates how the knight-errant would wander the land in search of adventures to prove his chivalric virtues, either in knightly duels (pas d'armes) or in some other pursuit of courtly love.
^As plural, knights-errant is most common, although the form knights-errants is also seen, e.g. in the article Graal in James O. Halliwell, Dictionary of Archaic and Provincial Words (1847).
^"Knight errant." The Canadian Oxford Dictionary. Ed. Barber, Katherine: Oxford University Press, 2004.