THESAURUS
underweight
avoirdupois, bantamweight, beef, beefiness, boniness, bony, deadweight, fatness, featherweight, flat, flat-chested, fleshless, fleshlessness, frailness, gangling, gangly, gaunt, gauntness, gawkiness, gawky, gravity, gross weight, haggardness, hatchet face, heaviness, heft, heftiness, lank, lankiness, lankness, lanky, lantern jaws, lean, lean-fleshed, lean-looking, leanness, lightweight, liveweight, meager, meagerness, neat weight, net, net weight, overbalance, overweight, paperiness, peakedness, ponderability, ponderosity, ponderousness, poorness, poundage, puniness, rawboned, scraggy, scrawniness, scrawny, skeletal, skin and bones, skinniness, skinny, slightness, spare, spareness, spidery, spindling, spindly, thin-bellied, thin-fleshed, tonnage, twigginess, twiggy, undersized, weight, weightiness