A shilling was a British coin that doesn't exist anymore, worth one-twentieth of a pound. Before 1971, when Britain switched to a decimal money system (like the one we use), a pound was divided into 20 shillings, and each shilling was divided into 12 pennies. If you've read books like A Christmas Carol or The Lion, the Witch and the Wardrobe, you might have noticed characters talking about shillings and wondering what they were worth.

The word can also be a verb: to shill means to promote something in a pushy or dishonest way, pretending to be an unbiased observer when you're actually being paid or have something to gain. If someone secretly works for a company but posts online pretending to be a regular customer praising its products, they're shilling for that company. A shill is someone who does this kind of deceptive promotion.