An Etymological Dictionary of the German Language/Annotated/plump
Appearance
plump, adjective, ‘plump, unwieldy, coarse,’ Modern High German only, from Low German and Dutch plomp, ‘thick, coarse, blunt’ hence in Swiss pflumpfig, with the High German permutation); from Dutch the word seems to have passed into English and Scandinavian as plump. The term plump was originally an imitation of sound.