pipe dream
noun
• an unattainable or fanciful hope or scheme.
• "free trade in international aviation will remain a pipe dream"
Similar:
fantasy,
false hope,
illusion,
delusion,
daydream,
unrealizable dream,
reverie,
mirage,
castle in the air,
castle in Spain,
chimera,
pie in the sky,
Origin:
late 19th century: referring to a dream experienced when smoking an opium pipe.
