The Collaborative International Dictionary of English v.0.48:

Brawn \Brawn\, n. [OF. braon fleshy part, muscle, fr. HG. br?to
   flesh, G. braten roast meat; akin to Icel. br?? flesh, food
   of beasts, AS. br?de roast meat, br?dan to roast, G. braten,
   and possibly to E. breed.]
   1. A muscle; flesh. [Obs.]
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            Formed well of brawns and of bones.   --Chaucer.
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   2. Full, strong muscles, esp. of the arm or leg, muscular
      strength; a protuberant muscular part of the body;
      sometimes, the arm.
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            Brawn without brains is thine.        --Dryden.
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            It was ordained that murderers should be brent on
            the brawn of the left hand.           --E. Hall.
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            And in my vantbrace put this withered brawn. --Shak.
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   3. The flesh of a boar; also, the salted and prepared flesh
      of a boar.
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            The best age for the boar is from two to five years,
            at which time it is best to geld him, or sell him
            for brawn.                            --Mortimer.
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   4. A boar. [Obs.] --Beau. & Fl.
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WordNet (r) 3.0 (2006):

brawn
    n 1: possessing muscular strength [syn: brawn, brawniness,
         muscle, muscularity, sinew, heftiness]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "brawn":
   all that lives, beef, beefiness, biosphere, biota, brawniness,
   ecosphere, elasticity, fiber, flesh, flora and fauna, heftiness,
   huskiness, involuntary muscle, living matter, living nature, might,
   muscle, muscles, muscularity, musculature, noosphere,
   organic matter, organic nature, organized matter, physique, plasm,
   power, robustness, sinew, sinewiness, sinews, strength, thew,
   thewiness, thews, tissue, tone, voluntary muscle