The Collaborative International Dictionary of English v.0.48:

Capacity \Ca*pac"i*ty\ (k[.a]*p[a^]s"[i^]*t[y^]), n.; pl.
   Capacities (-t[i^]z). [L. capacitus, fr. capax, capacis;
   fr. F. capacit['e]. See Capacious.]
   1. The power of receiving or containing; extent of room or
      space; passive power; -- used in reference to physical
      things.
      [1913 Webster]

            Had our great palace the capacity
            To camp this host, we all would sup together.
                                                  --Shak.
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            The capacity of the exhausted cylinder. --Boyle.
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   2. The power of receiving and holding ideas, knowledge, etc.;
      the comprehensiveness of the mind; the receptive faculty;
      capability of understanding or feeling.
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            Capacity is now properly limited to these [the mere
            passive operations of the mind]; its primary
            signification, which is literally room for, as well
            as its employment, favors this; although it can not
            be denied that there are examples of its usage in an
            active sense.                         --Sir W.
                                                  Hamilton.
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   3. Ability; power pertaining to, or resulting from, the
      possession of strength, wealth, or talent; possibility of
      being or of doing.
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            The capacity of blessing the people.  --Alex.
                                                  Hamilton.
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            A cause with such capacities endued.  --Blackmore.
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   4. Outward condition or circumstances; occupation;
      profession; character; position; as, to work in the
      capacity of a mason or a carpenter.
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   5. (Law) Legal or moral qualification, as of age, residence,
      character, etc., necessary for certain purposes, as for
      holding office, for marrying, for making contracts, wills,
      etc.; legal power or right; competency.
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   Capacity for heat, the power of absorbing heat. Substances
      differ in the amount of heat requisite to raise them a
      given number of thermometric degrees, and this difference
      is the measure of, or depends upon, what is called their
      capacity for heat. See Specific heat, under Heat.

   Syn: Ability; faculty; talent; capability; skill; efficiency;
        cleverness. See Ability.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

260 Moby Thesaurus words for "capacity":
   IQ, SRO, ability, ableness, accommodation, acumen, address,
   adeptness, adequacy, adroitness, airmanship, amplitude,
   apprehension, aptitude, artfulness, artisanship, artistry,
   bellyful, bent, brains, bravura, brilliance, brimful, brimming,
   bulging, bump, bumper, burden, bursting, caliber, capability,
   capableness, capaciousness, capacitance, capital, character,
   charge, chock-full, chuck-full, cleverness,
   collector junction capacitance, command, commodiousness,
   competence, competency, complement, comprehension, conception,
   condition, congested, consciousness, content, control,
   coordination, cordage, craft, craftsmanship, cram, cram-full,
   crammed, crush, cunning, deductive power, deftness, devices,
   dexterity, dexterousness, dextrousness, dimensions, diplomacy,
   disposable resources, dower, dowry, duty, efficacy, efficiency,
   emitter junction capacitance, endowment, equipment,
   esemplastic power, expansiveness, expertise, extensiveness,
   facility, faculties, faculty, farad, farci, fill, filled, finesse,
   fitness, flair, flush, footing, forte, full, full house,
   full measure, full to bursting, function, funds, genius, gift,
   grace, grip, handiness, horsemanship, ideation, ingeniousness,
   ingenuity, instinct, integrative power, intellect,
   intellectual gifts, intellectual grasp, intellectual power,
   intellectualism, intellectuality, intellectuals, intelligence,
   intelligence quotient, jam up, jam-packed, job, judgement, knack,
   know-how, knowledge, lading, limit, load, long suit, makings,
   marksmanship, mastership, mastery, means, measure, mental age,
   mental capacity, mental grasp, mental ratio, mentality, method,
   metier, might, mother wit, mouthful, native wit, natural endowment,
   natural gift, office, overfull, overstuffed, packed,
   packed like sardines, part, parts, perception, perceptiveness,
   perspicacity, place, plenary, position, post, potential, poundage,
   power, power of mind, powers, practical ability, proficiency,
   province, prowess, qualification, quality, quantity, quickness,
   rank, rationality, readiness, ready to burst, reasoning power,
   recourses, relation, replete, resistance capacitance, resorts,
   resource, resourcefulness, resources, responsibility, role, room,
   roominess, round, sanity, satiated, saturated, savoir-faire, savvy,
   scope of mind, seamanship, sense, senses, situation, size, skill,
   skillfulness, skinful, snootful, soaked, space, spaciousness,
   speciality, sphere, standing, standing room only, state, station,
   status, stock, stowage, strong flair, strong point, stuffed, style,
   sufficiency, supply, surfeited, susceptibility, swollen, tact,
   tactfulness, talent, talents, technical brilliance,
   technical mastery, technical skill, technique, the goods,
   the stuff, thinking power, timing, tonnage, topful, twin,
   understanding, virtuosity, volume, ways, ways and means,
   what it takes, wherewith, wherewithal, wit, wits, wizardry,
   workmanship