English is filled with all sorts of odd expressions, many of which inexplicably involve animals. You can be sick as a dog, sweating like a pig, and so hungry you could eat a horse. Given our history first as hunters and then as agriculturalists, perhaps it makes sense that our experience is colored by our relationship with the fauna of the world. So, what’s the deal with having a nest egg?

Let’s start with a basic definition. A “nest egg” refers to a sum of money that has been saved up, usually set aside for a particular purpose. Mr. and Mrs. Smith may have built up a “nest egg” for their son’s college education. That’s his college fund. Louise may have accumulated a rather sizable “nest egg” for an early retirement, because she has always lived below her means.

While few people would fault you for thinking that a “nest egg” and “savings” are one and the same, they’re technically not. The former is usually being set aside for a specific reason, like retirement. This is also why it’s technically different from a “rainy day fund” for emergency purposes.

But where did this term come from in the first place?

Apparently, it’s a reference to the old practice of placing a real or artificial egg in the nest of a hen. The idea, as hare-brained as it might sound, is that this was supposed to encourage the chicken to lay more eggs. This superstition dates back as far as the 14th century. Maybe it’s for good luck. Maybe it’s like how buskers might put some money in their guitar case before starting their performance or how some people “seed” their tip jar.

The connection between saving money and an actual hen’s nest is unclear. It might have to do with getting the egg back so you can use it later, like emptying the tip jar at the end of a shift. Using the term “nest egg” to refer to savings goes back to at least the late 17th century, so it’s hardly a modern creation.

So, if you want to build up a comfortable nest egg for retirement, don’t wait until your ducks are in a row to start setting some money aside. And remember not to put all your eggs in one basket and don’t count your chickens before they’re hatched. Otherwise, you could be in a for a “fowl” surprise.