"cold cash" vs. "hard cash"

Question

Context (New York Times):

Besides piling into Treasuries, institutional investors are also seeking out the safety of cold, hard cash, pouring billions into commercial bank accounts backed up by the Federal Deposit Insurance Corporation.

Dictionary.com:

cold cash: Also, hard cash . Actual currency (bills and coins); money immediately available, paid at the time of a purchase.

The Oxford Advanced Learner's Dictionary lists cold cash as American English, and hard cash as British English.

Is the OALD correct? Is there a difference between these two terms or not?

Answer 1

As aedia pointed out, in American English you are more likely to hear "cold, hard cash" than "cold cash" alone. In light of this, here are two Google Ngrams comparing cold cash, hard cash and cold, hard cash.

In American English:

In British English:

I realize that "hard cash" will include the counts of "hard cash" on its own, and "cold, hard cash". However, in both cases hard cash is far more likely. Using just "cold cash" and "hard cash" in the NGram discounts the use of both together. Therefore, it seems as if hard cash is more likely in both dialects of English.

Answer 2

A comparison on Google's Books Ngram viewer - American English vs British English - shows that cold cash is almost non-existing in British English but used quite extensively in American English.

So with the assumption that you can conclude anything from this, OALD is correct.