The Collaborative International Dictionary of English v.0.48:

Sinew \Sin"ew\, n. [OE. sinewe, senewe, AS. sinu, seonu; akin to
   D. zenuw, OHG. senawa, G. sehne, Icel. sin, Sw. sena, Dan.
   sene; cf. Skr. sn[=a]va. [root]290.]
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   1. (Anat.) A tendon or tendonous tissue. See Tendon.
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   2. Muscle; nerve. [R.] --Sir J. Davies.
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   3. Fig.: That which supplies strength or power.
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            The portion and sinew of her fortune, her marriage
            dowry.                                --Shak.
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            The bodies of men, munition, and money, may justly
            be called the sinews of war.          --Sir W.
                                                  Raleigh.
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   Note: Money alone is often called the sinews of war.
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The Collaborative International Dictionary of English v.0.48:

Sinew \Sin"ew\, v. t. [imp. & p. p. Sinewed; p. pr. & vb. n.
   Sinewing.]
   To knit together, or make strong with, or as with, sinews.
   --Shak.
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         Wretches, now stuck up for long tortures . . . might,
         if properly treated, serve to sinew the state in time
         of danger.                               --Goldsmith.
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WordNet (r) 3.0 (2006):

sinew
    n 1: a cord or band of inelastic tissue connecting a muscle with
         its bony attachment [syn: tendon, sinew]
    2: possessing muscular strength [syn: brawn, brawniness,
       muscle, muscularity, sinew, heftiness]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "sinew":
   amperage, arm, armipotence, authority, backbone, beef, beefiness,
   bite, bitingness, black power, brawn, brawniness, brute force,
   charge, charisma, clout, cogence, cogency, compulsion, cuttingness,
   dint, drive, duress, effect, effectiveness, effectuality,
   elasticity, energy, flower power, force, force majeure,
   forcefulness, full blast, full force, guts, heftiness, huskiness,
   impressiveness, incisiveness, influence, involuntary muscle,
   ligament, main force, main strength, mana, might, might and main,
   mightiness, mordancy, moxie, muscle, muscle power, muscularity,
   musculature, nervosity, nervousness, physique, pillar, pizzazz,
   poignancy, poop, potence, potency, potentiality, power, power pack,
   power structure, power struggle, powerfulness, prepotency,
   productiveness, productivity, puissance, pull, punch, push,
   sinewiness, sinews, stamina, steam, strength, strong arm,
   strong language, superiority, superpower, tendon, thew, thewiness,
   thews, tone, trenchancy, validity, vehemence, vigor, vigorousness,
   vim, virility, virtue, virulence, vitality, voluntary muscle,
   wattage, weight