The Collaborative International Dictionary of English v.0.48:

Brawny \Brawn"y\, a.
   Having large, strong muscles; muscular; fleshy; strong.
   "Brawny limbs." --W. Irving.
   [1913 Webster]

   Syn: Muscular; fleshy; strong; bulky; sinewy; athletic;
        stalwart; powerful; robust.
        [1913 Webster]

WordNet (r) 3.0 (2006):

brawny
    adj 1: (of a person) possessing physical strength and weight;
           rugged and powerful; "a hefty athlete"; "a muscular
           boxer"; "powerful arms" [syn: brawny, hefty,
           muscular, powerful, sinewy]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "brawny":
   able-bodied, adipose, athletic, beefy, big-bellied, bloated,
   blowzy, bosomy, broad-shouldered, bulky, burly, buxom, chubby,
   chunky, corpulent, distended, dumpy, fat, fattish, fleshy, full,
   gross, heavyset, hefty, hippy, husky, imposing, lusty, meaty,
   mighty, muscle-bound, muscular, obese, overweight, paunchy, plump,
   podgy, portly, potbellied, powerful, pudgy, puffy, pursy,
   red-blooded, robust, roly-poly, rotund, sinewy, square, squat,
   squatty, stalwart, stocky, stout, strapping, strong, swollen,
   thewy, thick-bodied, thickset, top-heavy, tough, tubby, vigorous,
   vital, well-built, well-fed, well-knit, well-set, well-set-up,
   wiry