The Collaborative International Dictionary
Quixotism \Quix"ot*ism\ (kw[i^]ks"[o^]t*[i^]z'm), n. That form of delusion which leads to extravagant and absurd undertakings or sacrifices in obedience to a morbidly romantic ideal of duty or honor, as illustrated by the exploits of Don Quixote in knight-errantry. See quixotic.
Wiktionary
n. 1 That form of delusion which leads to extravagant and absurd undertakings or sacrifices in obedience to a morbidly romantic ideal of duty or honor, as illustrated by the exploits of Don Quixote in knight-errantry. 2 quixotry.
WordNet
n. quixotic (romantic and impractical) behavior [syn: knight errantry]
Wikipedia
Quixotism ( or ) (adj. quixotic) is impracticality in pursuit of ideals, especially those ideals manifested by rash, lofty and romantic ideas or extravagantly chivalrous action. It also serves to describe an idealism without regard to practicality. An impulsive person or act might be regarded as quixotic.
Quixotism is usually related to "over-idealism", meaning an idealism that doesn't take consequence or absurdity into account. It is also related to naïve romanticism and to utopianism.
Usage examples of "quixotism".
It might have been that quixotism had inspired his infatuate gesture, but it might quite as conceivably have been everyday vanity or plain cussedness: a noble impulse to serve a pretty lady in distress, a spontaneous device to engage her interest, or a low desire to plague a personality as antipathetic to his own as that of a rattlesnake.
Quixotism in expecting that the public will ever pretend to understand his lucubrations or feel any interest in subjects of such sad and unkempt antiquity.