The Collaborative International Dictionary of English v.0.48:

Temperament \Tem"per*a*ment\, n. [L. temperamentum a mixing in
   due proportion, proper measure, temperament: cf. F.
   temp['e]rament. See Temper, v. t.]
   1. Internal constitution; state with respect to the relative
      proportion of different qualities, or constituent parts.
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            The common law . . . has reduced the kingdom to its
            just state and temperament.           --Sir M. Hale.
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   2. Due mixture of qualities; a condition brought about by
      mutual compromises or concessions. [Obs.]
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            However, I forejudge not any probable expedient, any
            temperament that can be found in things of this
            nature, so disputable on their side.  --Milton.
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   3. The act of tempering or modifying; adjustment, as of
      clashing rules, interests, passions, or the like; also,
      the means by which such adjustment is effected.
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            Wholesome temperaments of the rashness of popular
            assemblies.                           --Sir J.
                                                  Mackintosh.
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   4. Condition with regard to heat or cold; temperature. [Obs.]
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            Bodies are denominated "hot" and "cold" in
            proportion to the present temperament of that part
            of our body to which they are applied. --Locke.
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   5. (Mus.) A system of compromises in the tuning of organs,
      pianofortes, and the like, whereby the tones generated
      with the vibrations of a ground tone are mutually modified
      and in part canceled, until their number reduced to the
      actual practicable scale of twelve tones to the octave.
      This scale, although in so far artificial, is yet closely
      suggestive of its origin in nature, and this system of
      tuning, although not mathematically true, yet satisfies
      the ear, while it has the convenience that the same twelve
      fixed tones answer for every key or scale, C[sharp]
      becoming identical with D[flat], and so on.
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   6. (Physiol.) The peculiar physical and mental character of
      an individual, in olden times erroneously supposed to be
      due to individual variation in the relations and
      proportions of the constituent parts of the body,
      especially of the fluids, as the bile, blood, lymph, etc.
      Hence the phrases, bilious or choleric temperament,
      sanguine temperament, etc., implying a predominance of one
      of these fluids and a corresponding influence on the
      temperament.
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   Equal temperament (Mus.), that in which the variations from
      mathematically true pitch are distributed among all the
      keys alike.

   Unequal temperament (Mus.), that in which the variations
      are thrown into the keys least used.
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The Collaborative International Dictionary of English v.0.48:

Equal \E"qual\, a. [L. aequalis, fr. aequus even, equal; akin to
   Skr. ?ka, and perh. to L. unus for older oinos one, E. one.]
   1. Agreeing in quantity, size, quality, degree, value, etc.;
      having the same magnitude, the same value, the same
      degree, etc.; -- applied to number, degree, quantity, and
      intensity, and to any subject which admits of them;
      neither inferior nor superior, greater nor less, better
      nor worse; corresponding; alike; as, equal quantities of
      land, water, etc.; houses of equal size; persons of equal
      stature or talents; commodities of equal value.
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   2. Bearing a suitable relation; of just proportion; having
      competent power, abilities, or means; adequate; as, he is
      not equal to the task.
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            The Scots trusted not their own numbers as equal to
            fight with the English.               --Clarendon.
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            It is not permitted to me to make my commendations
            equal to your merit.                  --Dryden.
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            Whose voice an equal messenger
            Conveyed thy meaning mild.            --Emerson.
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   3. Not variable; equable; uniform; even; as, an equal
      movement. "An equal temper." --Dryden.
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   4. Evenly balanced; not unduly inclining to either side;
      characterized by fairness; unbiased; impartial; equitable;
      just.
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            Are not my ways equal?                --Ezek. xviii.
                                                  29.
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            Thee, O Jove, no equal judge I deem.  --Spenser.
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            Nor think it equal to answer deliberate reason with
            sudden heat and noise.                --Milton.
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   5. Of the same interest or concern; indifferent.
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            They who are not disposed to receive them may let
            them alone or reject them; it is equal to me.
                                                  --Cheyne.
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   6. (Mus.) Intended for voices of one kind only, either all
      male or all female; -- opposed to mixed. [R.]
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   7. (Math.) Exactly agreeing with respect to quantity.
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   Equal temperament. (Mus.) See Temperament.

   Syn: Even; equable; uniform; adequate; proportionate;
        commensurate; fair; just; equitable.
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WordNet (r) 3.0 (2006):

equal temperament
    n 1: the division of the scale based on an octave that is
         divided into twelve exactly equal semitones; "equal
         temperament is the system commonly used in keyboard
         instruments"