Definition of "blue-sky" [blue-sky]

• Unrealistic and impractical: "[The author] shows what is testable physics, what is philosphy's domain, and what is blue-sky nonsense” ( Ann Finkbeiner). (adjective)
• Having a cloudless sky; clear: a blue-sky day. (adjective)
• To hold or express unrealistic or impractical views, especially in estimating something. Often used with it. (verb-intransitive)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "He's applied what he learned in engaging with his Fed colleagues in "what I call blue-sky thinking, generating many ideas," he said."
• "The author of "The Wavewatcher's Companion" and "The Cloudspotter's Guide," Mr. Pretor-Pinney is the founder of the Cloud Appreciation Society, "a global organization that fights 'blue-sky thinking,' " which I had not realized could be considered bad."
• "The delightful, colorful, blue-river blue-sky "The Seine at Bercy" circa 1876-78—a copy of a painting by his Impressionist friend Armand Guillaumin—is about as Impressionist as Cézanne ever gets."