Q: I’m perplexed by the use of the phrase “pony up” to describe laying out money for something. What does the concept it describes have to do with ponies?
A: Since the early 19th century, “pony” has been a slang word for money in general, according to Cassell’s Dictionary of Slang.
Why “pony”? The dictionary notes that the word has usually referred to “relatively small sums, as a pony is a small horse.” And to come up with the pony, or “pony up” (circa 1824), meant to pay one’s debts or dues.
Eric Partridge’s A Dictionary of Slang and Unconventional English generally agrees. It describes “pony” as a term, circa 1810, for money, and goes along with the “small horse = small sum” explanation.
Partridge says “pony up” (“to pay a sum of money”) is a variant of an earlier expression, recorded in 1823, “post the pony.” (As far back as 1780 or so, to “post” meant to pay.)
The first published use of “pony up” cited in the Oxford English Dictionary is from an 1824 issue of the Atlantic Magazine: “Every man … vociferously swore that he had ponied up his ‘quarter.’ “