Because at one time, a “pair of pants” was two pieces of fabric and belted in the middle. Over the years, they were manufactured as one piece but the term remained.

Word History: One would not expect a word for a modern article of clothing to come ultimately from the name of a 4th-century Roman Catholic saint, but that is the case with the word pants. It can be traced back to Pantaleon, the patron saint of Venice. He became so closely associated with the inhabitants of that city that the Venetians were popularly known as Pantaloni. Consequently, among the commedia dell’arte’s stock characters the representative Venetian (a stereotypically wealthy but miserly merchant) was called Pantalone, or Pantalon in French. In the mid-17th century the French came to identify him with one particular style of trousers, a style which became known as pantaloons in English. Pantaloons was later applied to another style that came into fashion in the late 18th century, tight-fitting garments that had begun to replace knee breeches. After that pantaloons was used to refer to trousers in general. The abbreviation of pantaloons to pants met with some resistance at first; it was considered vulgar and, as Oliver Wendell Holmes put it, “a word not made for gentlemen, but ‘gents.'” First found in the writings of Edgar Allan Poe in 1840, pants has replaced the “gentleman’s word” in English and has lost all obvious connection to Saint Pantaleon.

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If his name had been Jimmy we would have called them “Jimmy’s” which, over time, would have become “Jimmys” then jimmies, etc. Because they (now) look and sound plural (rather than the original possessive) we would pluralize the adjectives as well and they would become a “pair of jimmies”, even though there is only one.

I would say even though we have two arms,we only have one chest,and since shirts are made for the coverage of the chest.

you can buy a shirt w/without sleeves,but pants with no legs wouldn’t be pants.

Lot’s of quirks in the English language….I’ve always wondered about this one:

If “rough” is pronounced RUFF………

Then why is “dough” pronounced DOE?

( shouldn’t that early morning treat be called “duffnuts”?)