Why is bra singular and panties plural?

Answer 1

"Bra" is short for "Brassiere," a French word that originally meant "a child's jacket with sleeves." It derives from an Old French word for "arms." Eventually, the word came to refer to the modern undergarment.

Thus, by replacing one word with the other, we go from "a brassiere" (singular) to "a bra" (also singular).

"Panties" derives from the word "pants," which was shortened from the original word "pantaloons," another French word. "Pantaloons" originally referred to a general *style* or *class* of garments either worn in Venice or assumed to have originated there. (That word was further derived from Saint Pantaleon, the patron saint of Venice.)

Again, by replacement, "he's wearning pantaloons" (plural) became "he's wearing pants" (also plural).

This unfortunately doesn't explain why people chose to shorten the term "Pantaloons" to "Pants" rather than "Pant," nor why "Brassiere" wasn't shortened to "Bras" (even though that is the Old French word for "arms").

Answer 2

This distinction likely comes from the historical development of the English language. The word "bra" is short for "brassiere," which entered English from the French language as a singular term. "Panties," on the other hand, is a plural form derived from "panty," which is used to refer to the undergarment for one leg. Over time, "panties" may have become the preferred term even when referring to a single garment for practical reasons or linguistic convention.