The Collaborative International Dictionary of English v.0.48:

Strength \Strength\, n. [OE. strengthe, AS. streng[eth]u, fr.
   strang strong. See Strong.]
   1. The quality or state of being strong; ability to do or to
      bear; capacity for exertion or endurance, whether
      physical, intellectual, or moral; force; vigor; power; as,
      strength of body or of the arm; strength of mind, of
      memory, or of judgment.
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            All his [Samson's] strength in his hairs were.
                                                  --Chaucer.
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            Thou must outlive
            Thy youth, thy strength, thy beauty.  --Milton.
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   2. Power to resist force; solidity or toughness; the quality
      of bodies by which they endure the application of force
      without breaking or yielding; -- in this sense opposed to
      frangibility; as, the strength of a bone, of a beam, of
      a wall, a rope, and the like. "The brittle strength of
      bones." --Milton.
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   3. Power of resisting attacks; impregnability. "Our castle's
      strength will laugh a siege to scorn." --Shak.
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   4. That quality which tends to secure results; effective
      power in an institution or enactment; security; validity;
      legal or moral force; logical conclusiveness; as, the
      strength of social or legal obligations; the strength of
      law; the strength of public opinion; strength of evidence;
      strength of argument.
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   5. One who, or that which, is regarded as embodying or
      affording force, strength, or firmness; that on which
      confidence or reliance is based; support; security.
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            God is our refuge and strength.       --Ps. xlvi. 1.
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            What they boded would be a mischief to us, you are
            providing shall be one of our principal strengths.
                                                  --Sprat.
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            Certainly there is not a greater strength against
            temptation.                           --Jer. Taylor.
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   6. Force as measured; amount, numbers, or power of any body,
      as of an army, a navy, and the like; as, what is the
      strength of the enemy by land, or by sea?
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   7. Vigor or style; force of expression; nervous diction; --
      said of literary work.
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            And praise the easy vigor of a life
            Where Denham's strength and Waller's sweetness join.
                                                  --Pope.
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   8. Intensity; -- said of light or color.
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            Bright Phoebus in his strength.       --Shak.
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   9. Intensity or degree of the distinguishing and essential
      element; spirit; virtue; excellence; -- said of liquors,
      solutions, etc.; as, the strength of wine or of acids.
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   10. A strong place; a stronghold. [Obs.] --Shak.
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   On the strength of, or Upon the strength of, in reliance
      upon. "The allies, after a successful summer, are too apt,
      upon the strength of it, to neglect their preparations for
      the ensuing campaign." --Addison.
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   Syn: Force; robustness; toughness; hardness; stoutness;
        brawniness; lustiness; firmness; puissance; support;
        spirit; validity; authority. See Force.
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The Collaborative International Dictionary of English v.0.48:

Strength \Strength\, v. t.
   To strengthen. [Obs.] --Chaucer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

strength
    n 1: the property of being physically or mentally strong;
         "fatigue sapped his strength" [ant: weakness]
    2: capability in terms of personnel and materiel that affect the
       capacity to fight a war; "we faced an army of great
       strength"; "politicians have neglected our military posture"
       [syn: military capability, military strength, strength,
       military posture, posture]
    3: physical energy or intensity; "he hit with all the force he
       could muster"; "it was destroyed by the strength of the
       gale"; "a government has not the vitality and forcefulness of
       a living man" [syn: force, forcefulness, strength]
    4: an asset of special worth or utility; "cooking is his forte"
       [syn: forte, strong suit, long suit, metier,
       specialty, speciality, strong point, strength] [ant:
       weak point]
    5: the power to induce the taking of a course of action or the
       embracing of a point of view by means of argument or
       entreaty; "the strength of his argument settled the matter"
       [syn: persuasiveness, strength] [ant: unpersuasiveness]
    6: the amount of energy transmitted (as by acoustic or
       electromagnetic radiation); "he adjusted the intensity of the
       sound"; "they measured the station's signal strength" [syn:
       intensity, strength, intensity level]
    7: capacity to produce strong physiological or chemical effects;
       "the toxin's potency"; "the strength of the drinks" [syn:
       potency, effectiveness, strength]
    8: the condition of financial success; "the strength of the
       company's stock in recent weeks" [ant: weakness]
    9: permanence by virtue of the power to resist stress or force;
       "they advertised the durability of their products" [syn:
       lastingness, durability, enduringness, strength]

Moby Thesaurus II by Grady Ward, 1.0:

221 Moby Thesaurus words for "strength":
   ability, amount, amperage, ampleness, amplitude, aptitude, arm,
   armipotence, asset, authoritativeness, authority, backbone, beef,
   bite, bitingness, black power, body, boundlessness, brawn,
   brawniness, brute force, bulk, burden, charge, charisma, clout,
   cogence, cogency, cohesiveness, compulsion, concentration,
   concreteness, core, cuttingness, demonic energy, density,
   determination, dint, drive, durability, duress, dynamism, effect,
   effectiveness, effectuality, endurance, energy, enormity,
   enormousness, ergal, expanse, extent, firmness, fixity of purpose,
   flower power, force, force majeure, forcefulness, formidableness,
   fortitude, full blast, full force, fullness, gameness, gaminess,
   gift, gigantism, gist, grandeur, grandness, great scope, greatness,
   grit, guts, gutsiness, haleness, hardiness, hardness, healthiness,
   heartiness, high flavor, highness, hugeness, immensity,
   impressiveness, incisiveness, infinity, influence, infrangibility,
   intensity, intestinal fortitude, intrepidity, iron will,
   kinetic energy, largeness, lastingness, leatherlikeness, longevity,
   lustiness, magisterialness, magnitude, main force, main strength,
   mana, mass, materiality, matter, measure, measurement, meat, might,
   might and main, mightiness, moral courage, moral fiber, mordancy,
   moxie, muchness, muscle, muscle power, nerve, nervosity,
   nervousness, numbers, palpability, perseverance, persistence,
   pertinacity, pith, pizzazz, plenitude, pluck, poignancy,
   ponderability, poop, potence, potency, potential energy,
   potentiality, power, power pack, power structure, power struggle,
   powerfulness, prepotency, prodigiousness, productiveness,
   productivity, puissance, pull, punch, purport, push, quantity,
   quantum, rankness, reliability, resistance, resoluteness,
   resolution, robustness, ropiness, ruggedness, security, sense,
   sinew, sinewiness, solidity, soundness, spunk, stability,
   stableness, stamina, steadiness, steam, stiffness, stoutness,
   strength of mind, strength of purpose, strenuousness, stringiness,
   strong arm, strong language, strong point, strongness,
   stubbornness, stupendousness, sturdiness, substance,
   substantiality, substantialness, sum, sum and substance,
   superiority, superpower, talent, tangibility, tenaciousness,
   tenacity, toughness, tremendousness, trenchancy, unbreakability,
   unbreakableness, validity, vastness, vehemence, vigor,
   vigorousness, vim, virility, virtue, virulence, viscidity,
   vitality, wattage, weight, whole, will, will of iron, will power