of persons, "extravagantly chivalrous, absurdly romantic," abstractly, "striving for an unattainable or impractical ideal," 1791, from Don Quixote, the romantic, impractical hero of Cervantes' satirical novel "Don Quixote de la Mancha" (1605; in English translation by 1620). Don Quixote as the type of anyone attempting the impossible or holding visionary but impossible ideals is in English from 1670s.
His name literally means "thigh," also "a cuisse" (a piece of armor for the thigh), in Modern Spanish quijote, from Latin coxa "hip" (see coxa). Related: Quixotical; quixotically.
Cervantes smiled Spain's chivalry away;
A single laugh demolish'd the right arm
Of his own country; — seldom since that day
Has Spain had heroes.
[Byron, "Don Juan"]