Sentence:  In short, his wits being quite gone, [Don Quixote] hit upon the strangest notion that ever madman in this world hit upon, and that was that he fancied it was right and requisite, as well for the support of his own honour as for the service of his country, that he should make a <WSD>knight-errant</WSD> of himself, roaming the world over in full armour and on horseback in quest of adventures, and putting in practice himself all that he had read of as being the usual practices of knights-errant; righting every kind of wrong, and exposing himself to peril and danger from which, in the issue, he was to reap eternal renown and fame. 
Meaning of the word marked with <WSD> tags:  A knight in a medieval romance who wanders in search of adventure and opportunities to prove his chivalry.