The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with flat broke
stone or stony broke. Completely penniless. For example, I can't help you—I'm flat broke, or He's stone broke again. The first term dates from the mid-1800s and uses flat in the sense of “completely” or “downright.” The variant dates from the late 1800s.