body part vs underpart

Other hyponyms of body part include saddle, horseback, dock, ambulacrum, withers, cannon, shank, loin, lumbus, croup, croupe, hindquarters, rump, gaskin, flank, thorax, apparatus, adnexa, annexa, area, region, dilator, groove, vallecula, partition, external body part, anatomical structure, bodily structure, body structure, complex body part, structure, fornix, system, ampulla, tissue, mentum, organ, venter, energid, protoplast, appendage, outgrowth, process, lobe, rectum, shoulder, body, torso, trunk, chest, pectus, thorax, thorax, hip, haunch, abdomen, belly, stomach, venter, dorsum, back, dorsum, small, arse, ass, backside, behind, bottom, bum, buns, butt, buttocks, can, derriere, fanny, fundament, hind end, hindquarters, keister, nates, posterior, prat, rear, rear end, rump, seat, stern, tail, tail end, tooshie, tush, buttock, cheek, stump, shank, shin, toe, articulatio, articulation, joint, loins, feature, lineament, rudiment.