Fun things learned in my honors history class.
I’m going to have to add this to the fifty other reasons I’ve seen given for the origin of the term “flapper”…it’s not too probable, though - flappers did wear under garments, including in some instances corsets. If they had the slight figure for it they wore a brassiere (not very supportive - really a strip of fabric with some ruching in the middle). Some wore bust flatteners to get the right look. Daring flappers in the early twenties did sometimes “park” their corsets or girdles at dances, checking them in with their coats!
Other suggested origins for the term include the supposed resemblence of the Charleston to a flapping bird (unlikely, as the term predates the Charleston), or the habit young women had of wearing their rubber galoshes open so that they flapped. The term seems to have originated at least in the teens, and possibly in the UK, where dresses for females in the supposed awkward, gawky stage between childhood and adulthood were called flapper dresses. Young women were supposed to be like birds in the nest, “flapping.”