Why is the opening on men’s trousers called a “fly”?
Before your speculation starts to soar too high, please note that “fly” refers, not to the zipper, but to the piece of fabric that covers the zipper.
“Fly,” derived from the Old English “flowan” (to flow), has acquired many meanings over the centuries, e.g., a winged insect, a baseball hit high into the air, the space above a theater stage, and a 1960s word for “cool.”
“Fly” also came to mean “something attached by one edge,” like a flag or banner flying from a rope or pole. With this meaning in mind, 19th-century tailors used the term “fly” for a flap of cloth attached at one end to cover an opening in a garment.
If you’re wearing a pair of pants right now, you can sneak a peek at your fly and see the “flap” (fly) covering the zipper. Warning: Do not do this if anyone else is around.
Interestingly, “fly” seems to be used exclusively for the opening on men’s trousers. Has one woman ever told another that her “fly” (or “barn door”) is open? I think not.
But, then again, I’m a guy; maybe women have a secret nonverbal code or glance to convey that message.
Meanwhile, let’s take a fast look at the fascinating origins of two other words for fasteners.
Zipper — When this ingenious mechanism first appeared during the late 1800s, it was called a “clasp locker” or “hookless fastener.” But when the B.F. Goodrich company introduced a boot featuring the device during the 1920s, a company exec reportedly slid the tab up and down, noticed the “zip” sound this made, and exclaimed, “Zip ‘er up!”
So B.F. Goodrich called the boots “zipper boots” and trademarked the name “zipper” in 1925. This mechanism proved so popular that the device itself came to be called a “zipper,” which soon zipped into the popular lexicon.
Velcro — In 1948, the Swiss engineer Georges de Mestral took a nature hike and returned with his trousers (including, presumably, his fly) covered with burrs. After examining these prickly hitchhikers under a microscope, he noticed they had tiny hooks that clung tenaciously to the small loops of thread in his pants.
Inspired, he devised two strips of cotton fabric that stuck together because one had tiny hooks and one had tiny loops. He named his invention “Velcro,” a combination of the French “velours” (velvet) and “croché” (hook).
Soon the generic name “velcro” jumped into common parlance, where it, well, stuck.
