“And a cool four thousand, Pip!”

“Well, old chap,” said Joe, “it do appear that she had settled the most of it, which I meantersay tied it up, on Miss Estella. But she had wrote out a little coddleshell in her own hand a day or two afore the accident, leaving a cool four thousand to Mr. Matthew Pocket. And why, do you suppose, above all things, Pip, she left that cool four thousand unto him? ‘Because of Pip’s account of him the said Matthew.’ I am told by Biddy, that air the writing,” said Joe, repeating the legal turn as if it did him infinite good, “‘account of him the said Matthew.’ And a cool four thousand, Pip!”

I never discovered from whom Joe derived the conventional temperature of the four thousand pounds, but it appeared to make the sum of money more to him, and he had a manifest relish in insisting on its being cool.

Charles Dickens, Great Expectations (1861)

Why cool? The Oxford English Dictionary is unable to explain the conventional temperature:

colloq. Used to emphasize the size of a quantity, orig. and chiefly a sum of money. Originally preceded by a with hundred or thousand; subsequently also with any numeral.

More helpful: the OED notes a suggestion in the New English Dictionary (1893) that the word meant “perhaps originally ‘deliberately or calmly counted, reckoned, or told,’ and hence ‘all told,’ ‘entire,’ ‘whole.’” The earliest OED citation — “a cool Thousand” (1721) — is from Colly Cibber, now remembered as a target of Alexander Pope’s mockery in The Dunciad (1743).

[Coddleshell: codicil.]