An empty wish or promise, as in His dream of being hired as a sports editor proved to be pie in the sky. This expression was first recorded in 1911 in a rallying song of a union, the International Workers of the World (or "Wobblies"): "Work and pray, live on hay, you'll get pie in the sky when you die."

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Company. All rights reserved.