Unmistakably valid money, as distinct from checks, promises, etc; Hard Cash: The place wants payment in cold cash, nothing less
[1884+; fr the notion that definite and inalterable things, like gold and silver coins, are cold and hard]
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 cold cash
hard cash. Actual currency (bills and coins); money immediately available, paid at the time of a purchase. For example, Will you lower the price if I pay in cold cash instead of using a credit card? or We have only a limited amount of hard cash—the rest is in accounts receivable.
[ First half of 1900s