means The part of the human body between the ribs and the hips, usually the narrowest portion of the torso, or the corresponding section of a garment.

from From Middle English 'wast,' built on the Old English root that gave us 'wax' in its older sense of 'to grow' — the waist was literally the place where the body 'grows' or reaches its full size. A cousin to that same growth-word lurks in 'waxing' moons. Its much later spelling twin, 'waste,' is unrelated, though English never seems to mind the confusion.