What is the Plural of 'Money?'
In most instances, we treat money as a mass noun or noncount noun—just like oxygen or mud or honesty. You can't have a single mud or four honesties, and in the same vein, we don't say a money or one money or twenty-six moneys. Even though it can be composed of discrete bills and coins, countable dollars and cents, the concept of money is treated as a mass in English. You either have money or you don't.
However, like common mass nouns such as water and sand, there are occasions when money is inflected with a standard plural, like any count noun. It tends to occur when the reference is to discrete sums of money, obtained from a particular source or allocated to a particular cause.
The spelling in these instance can be moneys or, more commonly, monies:
Some of the 2009 stimulus monies for high-speed rail should end up in the California project and more may be coming.
—James McCommons, Waiting on a Train, 2009
Under Oregon's unique "kicker" law, if general fund revenue tops projections by more than 2 percent, the entirety of the above-projection moneys goes back to taxpayers in the form of a rebate.
—Connor Radnovich, The Statesman Journal (Salem, Ore.), 23 Aug. 2017
The West Virginia Department of Health and Human resources announced it will use $22 million in settlement monies received from drug distributors to combat the drug epidemic in West Virginia.
—Kara Leigh Lofton, West Virginia Public Broadcasting, 21 Aug. 2017
The mood today is slightly less worshipful, and the reason is simple. Voters are tired of using public monies to enrich millionaire sports owners.
—Carl Hiaasen, Kick Ass, 1999
Most nouns that end in –ey take a standard -s plural: monkeys, chimneys, attorneys, turkeys. Moneys naturally follows that pattern. Some usage critics decry the spelling monies because it encourages a pronunciation akin to the plural nouns ponies or cronies, as though the singular noun were actually spelled mony. These days, however, monies is in fact the more common spelling.