Source : Webster's Revised Unabridged Dictionary (1913)

   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.

   {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.

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.

   2. Bearing a suitable relation; of just proportion; having
      competent power, abilities, or means; adequate; as, he is
      not equal to the task.

            The Scots trusted not their own numbers as equal to
            fight with the English.               --Clarendon.

            It is not permitted to me to make my commendations
            equal to your merit.                  --Dryden.

            Whose voice an equal messenger Conveyed thy meaning
            mild.                                 --Emerson.

   3. Not variable; equable; uniform; even; as, an equal
      movement. ``An equal temper.'' --Dryden.

   4. Evenly balanced; not unduly inclining to either side;
      characterized by fairness; unbiased; impartial; equitable;
      just.

            Are not my ways equal?                --Ezek. xviii.
                                                  29.

            Thee, O Jove, no equal judge I deem.  --Spenser.

            Nor think it equal to answer deliberate reason with
            sudden heat and noise.                --Milton.

   5. Of the same interest or concern; indifferent.

            They who are not disposed to receive them may let
            them alone or reject them; it is equal to me.
                                                  --Cheyne.

   6. (Mus.) Intended for voices of one kind only, either all
      male or all female; -- opposed to mixed. [R.]

   7. (Math.) Exactly agreeing with respect to quantity.

   {Equal temperament}. (Mus.) See {Temperament}.

   Syn: Even; equable; uniform; adequate; proportionate;
        commensurate; fair; just; equitable.

Source : WordNet®

equal temperament
     n : 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"