A grandson asked where this expression came from. The Phrase Finder writes that a popular but incorrect origin is that the Royal Navy served meals on square wooden plates. The expression is of U.S. origin and is based on the use of the word “square” to mean proper and honest. The earliest written reference was in a November 1856 advertisement in the newspaper The Mountain Democrat for the Hope and Neptune restaurant. The ad promised a “square meal” of “oyster, chicken, and game prepared at short notice.”