quixotic

Quixotic comes from Spanish Quixote, the surname of Don Quixote, the title character of Miguel de Cervantes' novel, combined with the suffix -ic.

The word simply took the name of Cervantes' idealistic, impractical knight and turned it into an adjective describing behavior like his.

It shares its root with the name Don Quixote itself, the character whose exploits gave English this word.