John, an excellent place to look up synonyms and antonyms is the Thesaurus. Put this in your favorite places for future reference.
Synonyms lean, skinny, slender, slim, spare
Related words angular, bony, rawboned, scraggy, scrawny, sinewy; lank, lanky, rangy, reedy, spindling, spindly, twiggy, waspish, weedy, willowy, wiry; anorexic, cadaverous, emaciated, gaunt, haggard, pinched, skeletal, wasted, wizened; puny, meager ( or meagre), slight
Near Antonyms beefy, bulky, chunky, fleshy, heavy, heavyset, stocky, stout, thick, thickset, weighty; brawny, burly, husky; dumpy, pudgy, roly-poly, squat, stubby; paunchy, potbellied; flabby, soft; buxom; fleshed-out, full, round
Antonyms chubby, corpulent, fat, gross, obese, overweight, plump, portly, rotund, tubby