1. Resembling or befitting Don Quixote
2. Extravagantly chivalrous or romantic; visionary, impractical, or impracticable
3. Impulsive and often rashly unpredictable
This word is obviously based on the character Don Quixote from 'The Ingenious Gentleman Don Quixote of La Mancha (or 'El Ingenioso Hidalgo Don Quijote de la Mancha' if you speak Spanish, which I don't) by Miguel de Cervantes. Quixote is apparently the Anglicized spelling of Quijote, which means "thigh" and derives from Latin coxa ("hip").
I've never read the book, but this print: