Why is the zipper on a part of pants called a fly ?

Why are zippers on pants called flies ?

That pretty much says it all.


It’s not. The zipper is called a zipper. The fly is the opening in the front of the pants, whether with a zipper, buttons, velcro, or open to the elements.

Properly speaking, the fly is the flap of cloth covering the opening, and is etymologically related to other protective flaps of cloth, such as a tent fly.

A fly was a fly long before the zipper came into usage-----and ,if you go back far enough in time ,it was just a long flap that was tucked into the opening for decency and comfort.

Sorta like a tent flap.

OK, so why is the opening called a fly?

Originally it probably wasn’t called a fly. but it might have become so through common usage-----since it was the place where the fly was located.

Open your fly—close your fly----your fly is open —your fly is closed.

Or they coulda just said,“Hey-----the hole in y’pants is open-close yer fly,guy!”

I’ll contribute a few facts from the OED. I don’t promise you that my surmises are correct, but so be it.

The word fly(flies) appears in theater usage in England in 1805.

In that same time frame(1810) we see that the roof of a tent was referred to with the same spelling(flies):

The fly on a pair of pants appears in 1844

in a military list of regulations.

Not hard to imagine that military type who lived in and pitched tents might coin the term “fly” to apply to the flap that covered the opening in their trousers.

Every once in a while, something flies out of those things


Just a conjecture. Couldn’t it have anything to do with flying a flag?