mid-13c., "coinage, metal currency," from Old French monoie "money, coin, currency; change" (Modern French monnaie), from Latin moneta "place for coining money, mint; coined money, money, coinage," from Moneta, a title or surname of the Roman goddess Juno, in or near whose temple money was coined; perhaps from monere "advise, warn" (see monitor (n.)), with the sense of "admonishing goddess," which is sensible, but the etymology is difficult. Extended early 19c. to include paper money.
To make money "earn pay" is first attested mid-15c. Highwayman's threat your money or your life first attested 1841. Phrase in the money (1902) originally meant "one who finishes among the prize-winners" (in a horse race, etc.). The challenge to put (one's) money where (one's) mouth is is first recorded 1942, American English. money-grub "one who is sordidly intent on amassing money" is from 1768. The image of money burning a hole in someone's pocket is attested from 1520s.