The reason is that originally, underwear (or undergarments) was singular and came from the phrase “to go under one’s clothes.” But panties, originally pantalettes, were popular as a separate garment that would cover the legs as well as the crotch. So because of what they covered and where they were worn, it became plural.
Bra, on the other hand, started out as a fashion term for what would now be called a brassiere. Brassière is singular in French, and it comes from “brassiéres” which was a word for a woman’s elbow-length gloves. So bras were originally not thought of as garments to be worn under clothing but rather outside clothing, to provide support (and to enhance the bust). And that’s why bras has been singular ever since.
Tags: history, language, lingerie, Pantalettes, Questions, singular verb, why is bra singular but panties plural?-where do undergarments come from?-The Language of Fashion and Power-Tightlacing: Two Hundred Years of the Corset by Valerie Steele. The Corset: A Cultural History by Valerie Steele. The Corset Mystique: The Myth of Beauty by Elizabeth Kendall. Girdles and Bras from Victoria’s Secret. How Much Did Victoria’s Secret Profit From Under-the-Bust Lingerie in 2016? Victoria’s Secret Brings Bras and Bikinis Back to Stores. How Much Does Victoria’s Secret Make Selling Lingerie? Victoria’s Secret Balances Marketing Trends with Sales Growth. Lingerie Market Takes a Hit as Sales Decline.