A fantastic but vain hope (from fantasies induced by the opium pipe):
— I have this pipe dream about being emperor of the universe.

synonym: dream.

Roget 515: imagination; originality; invention; fancy; inspiration; verve.    warm imagination, heated imagination, excited imagination, sanguine imagination, ardent imagination, fiery imagination, boiling imagination, wild imagination, bold imagination, daring imagination, playful imagination, lively imagination, fertile imagination, fancy.    mind's eye;" such stuff as dreams are made of" [Tempest]. ideality, idealism; romanticism, utopianism, castle-building.    dreaming; phrensy^†, frenzy; ecstasy, extasy^†; calenture etc. (delirium) 503^†; reverie, trance; day dream, golden dream; somnambulism.    conception, Vorstellung [G.], excogitation^†, a fine frenzy;" cloudland^†, dreamland; flight of fancy, fumes of fancy; thick coming fancies" [Macbeth]; creation of the brain, coinage of the brain; imagery.    conceit, maggot, figment, myth, dream, vision, shadow, chimera; phantasm, phantasy; fantasy, fancy; whim, whimsey^†, whimsy; vagary, rhapsody, romance, gest^†, geste^†, extravaganza; air drawn dagger, bugbear, nightmare.    flying Dutchman, great sea serpent, man in the moon, castle in the air, pipe dream, pie-in-the-sky, chateau en Espagne [Fr.]; Utopia, Atlantis^†, happy valley, millennium, fairyland; land of Prester John, kindgom of Micomicon; work of fiction etc. (novel) 594; Arabian nights^†; le pot au lait [Fr.]; dream of Alnashar etc. (hope) 858^†.    illusion etc. (error) 495; phantom etc. (fallacy of vision) 443; Fata Morgana etc. (ignis fatuus) [Lat.] 423; vapor etc. (cloud) 353; stretch of the imagination etc. (exaggeration) 549; mythogenesis^†.    idealist, romanticist, visionary; mopus^†; romancer, dreamer; somnambulist; rhapsodist etc. (fanatic) 504; castle-buildier, fanciful projector.    ... show more

Dutch: luchtkasteel, toekomstdroom
Polish: miraż, mrzonka, złudzenie, utopia