pipe dream

• pipedream

From the fantasies experienced when smoking an opium pipe, equivalent to pipe +‎ dream. First attested in the 1800s; compare Old English pīpdrēam (“the sound or music of a pipe”), which is an identical yet separate and unconnected formation.

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pipe dream (plural pipe dreams)

1. (idiomatic) A plan, desire, or idea that will not likely work; a near impossibility.

   Synonyms: castle in the air, pie in the sky

   I think that his plan to become a professional athlete is a pipe dream and that he should stay in school.

   • 1962 December, “Dr. Beeching previews the plan for British Railways”, in Modern Railways, page 376:

     Only a year ago it would have needed a "super-Micawber" to be optimistic that the railways would once again pay their way. But it was no longer a pipe dream that B.R. could make a profit, the way to do it was now clear.

• “pipe dream”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.