means A one-piece garment that joins top and trousers into a single outfit, worn for fashion, work, or anything requiring you to commit to a look from neck to ankle.

from Born of the air: the word dates to the 1910s–1920s, coined for the literal garment parachutists and skydivers wore to jump from planes — a single suit you could leap in without anything flapping loose. From those daredevils it drifted into pilots' and mechanics' wardrobes, then onto runways, where the practicality of one zipper became, somehow, a statement.