means A one-piece garment combining a top and shorts, worn by babies, children, or adults for play or comfort.

from From the verb 'romp,' meaning to play boisterously, which itself is probably an alteration of 'ramp' — an old word for rearing up or leaping about, once used of rampaging animals. A 'romper' was first a child's play-suit, named for the rough-and-tumble it was built to survive; the adult fashion 'romper' borrowed the name much later.