The Collaborative International Dictionary of English v.0.48:

Beefy \Beef"y\, a.
   Having much beef; of the nature of beef; resembling beef;
   fleshy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

beefy
    adj 1: muscular and heavily built; "a beefy wrestler"; "had a
           tall burly frame"; "clothing sizes for husky boys"; "a
           strapping boy of eighteen"; "`buirdly' is a Scottish
           term" [syn: beefy, burly, husky, strapping,
           buirdly]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "beefy":
   adipose, big-bellied, bloated, blowzy, bosomy, bouncing, brawny,
   burly, buxom, chubby, chunky, corpulent, distended, doughty, dumpy,
   fat, fattish, fleshy, forceful, forcible, forcy, full,
   full-blooded, full-strength, gross, gutsy, gutty, hale, hard,
   hard as nails, hardy, hearty, heavyset, hefty, hippy, husky,
   imposing, iron-hard, lusty, meaty, mighty, nervy, obese, obstinate,
   overweight, paunchy, plump, podgy, portly, potbellied, potent,
   powerful, pudgy, puffy, puissant, pursy, red-blooded, robust,
   robustious, roly-poly, rotund, rugged, square, squat, squatty,
   stalwart, steely, stocky, stout, strapping, strong,
   strong as brandy, strong as strong, strong-willed, sturdy, swollen,
   thick-bodied, thickset, top-heavy, tubby, vigorous, well-fed