a pipe dream

pipe dream

A dream or idea that is impossible to accomplish. Many say that achieving world peace is a pipe dream because human beings are so flawed in their logic and emotions.
See also: dream, pipe
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

a pipe dream

If you describe something that someone wants to do or happen as a pipe dream, you mean that it is not realistic and will probably not happen. Oh, Toddy, it's a pipe dream. The banks won't lend you that sort of money. He said the figures showed that a third runway at the airport remained a pipe dream. Note: This expression refers to the sort of idea that someone is likely to have when they are smoking a drug in a pipe.
See also: dream, pipe
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012

a ˈpipe dream

a hope, belief, plan, etc. that will probably never come true: She’s got this pipe dream about being a pop star.This expression refers to smoking the drug opium, which makes you sleep and gives you powerful dreams.
See also: dream, pipe
Farlex Partner Idioms Dictionary © Farlex 2017
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References in periodicals archive ?
A pipe dream of size n is a filling of the staircase shape (n - 1, ..., 2, 1) where each box contains two crossing pipes + or two turning pipes [??].
FOR ALL WE HEAR of the rapid pace of technological development, many users in the real world consider the following truths to be self-evident: Your notebook computer never has enough juice to finish a job on the go, and commercial fuel cells are a pipe dream decades away from realization.