Shylock: as banker
In answer to this question, a child, some "statesmen," and many traders will say that money is gold, silver, and bank-bills, with copper or nickel coins for small transactions. Certainly it is. But at different periods in the progress of mankind it has been almost everything else.
Sheep and cattle were the earliest money in general use to any large extent. In Sparta, where Lycurgus determined to breed a race of hardy soldiers with few wants and no luxuries, he would have nothing but iron for his "medium of exchange" a cart-load for ten dollars. In ancient Britain, slaves were used for coins and were named "living money." Thus the ancestors of Jay Gould, perhaps, were passed from hand to hand to buy pork.
When Rome first came to need a legal-tender, Servius Tullius coined copper, imprinting on the pieces images of domestic animals. These were the "gold basis" behind the fiat-tokens. Rome had no monetary use for gold until two centuries before the Christian era. She coined silver a little earlier. Her great rival, Carthage, used leather, turned into some form of treasury imprints. When Nicolo and Maffeo Polo went from Venice to Cathay, they found that money there consisted of the inner bark of a tree, cut in circles, bearing the stamp of the king. It was a very effective "legal tender"; for to counterfeit this money or to refuse it was death.
Glass-coin was once the currency of Arabia and codfish the "gold-standard" of Newfoundland. Platinum was discontinued in Russia as late as 1845, and soap, at the Castle of Perota in Mexico after 1847. Africa on occasion passes strips of cotton-cloth as Bank-of-England notes, reemable on demand in uses of modest adornment. Once, in Massachusetts, when Indians were numerous and lead was scarce, musket-balls became money, of the highest "intrinsic value." Gold was "a seventy-cent dollar" beside a bit of junk for bullets. In 1732 tobacco was a legal tender in Maryland and tenpenny nails were the small-change of Scotland in 1776. Before the good Mr. George W. Childs converted Philadelphia into a large village-paradise, turnips circulated there instead of copper cents. It was as late as 1865 and Mr. Childs's own paper, the "Ledger," is authority for the fact.
But the line of history is long, not to say endless on this subject. Almost every animal of human use, many vegetables and cereals, nearly all the metals, and a great variety of minerals have been employed at different times among different nations to exchange commodities: that is to say, all these things have constituted money.
What then, again, is this thing? From facts alone, with no dependence on theory, we have already found the answer. Money is some generally recognized embodiment or some legally-imposed certificate of purchasing-power.