The Collaborative International Dictionary of English v.0.48:

Descant \Des"cant\ (d[e^]s"k[a^]nt), n. [OF. descant, deschant,
   F. d['e]chant, discant, LL. discantus, fr. L. dis + cantus
   singing, melody, fr. canere to sing. See Chant, and cf.
   Descant, v. i., Discant.]
   1. (Mus.)
      (a) Originally, a double song; a melody or counterpoint
          sung above the plain song of the tenor; a variation of
          an air; a variation by ornament of the main subject or
          plain song.
      (b) The upper voice in part music.
      (c) The canto, cantus, or soprano voice; the treble.
          --Grove.
          [1913 Webster]

                Twenty doctors expound one text twenty ways, as
                children make descant upon plain song.
                                                  --Tyndale.
          [1913 Webster]

                She [the nightingale] all night long her amorous
                descant sung.                     --Milton.
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   Note: The term has also been used synonymously with
         counterpoint, or polyphony, which developed out of the
         French d['e]chant, of the 12th century.
         [1913 Webster]

   2. A discourse formed on its theme, like variations on a
      musical air; a comment or comments.
      [1913 Webster]

            Upon that simplest of themes how magnificent a
            descant!                              --De Quincey.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Descant \Des*cant"\ (d[e^]s*k[a^]nt"), v. i. [imp. & p. p.
   Descanted; p. pr. & vb. n. Descanting.] [From descant;
   n.; or directly fr. OF. descanter, deschanter; L. dis- +
   cantare to sing.]
   1. To sing a variation or accomplishment.
      [1913 Webster]

   2. To comment freely; to discourse with fullness and
      particularity; to discourse at large.
      [1913 Webster]

            A virtuous man should be pleased to find people
            descanting on his actions.            --Addison.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Figurate \Fig"ur*ate\, a. [L. figuratus, p. p. of figurare. See
   Figure.]
   1. Of a definite form or figure.
      [1913 Webster]

            Plants are all figurate and determinate, which
            inanimate bodies are not.             --Bacon.
      [1913 Webster]

   2. Figurative; metaphorical. [Obs.] --Bale.
      [1913 Webster]

   3. (Mus.) Florid; figurative; involving passing discords by
      the freer melodic movement of one or more parts or voices
      in the harmony; as, figurate counterpoint or descant.
      [1913 Webster]

   Figurate counterpoint or Figurate descant (Mus.), that
      which is not simple, or in which the parts do not move
      together tone for tone, but in which freer movement of one
      or more parts mingles passing discords with the harmony;
      -- called also figural, figurative, and figured
      counterpoint or descant (although the term figured is
      more commonly applied to a bass with numerals written
      above or below to indicate the other notes of the
      harmony).

   Figurate numbers (Math.), numbers, or series of numbers,
      formed from any arithmetical progression in which the
      first term is a unit, and the difference a whole number,
      by taking the first term, and the sums of the first two,
      first three, first four, etc., as the successive terms of
      a new series, from which another may be formed in the same
      manner, and so on, the numbers in the resulting series
      being such that points representing them are capable of
      symmetrical arrangement in different geometrical figures,
      as triangles, squares, pentagons, etc.

   Note: In the following example, the two lower lines are
         composed of figurate numbers, those in the second line
         being triangular, and represented thus:
         . 1, 2, 3, 4, etc. . . . 1, 3, 6, 10, etc. . . . . . .
         . etc. 1, 4, 10, 20, etc . . . . . . . . . . . .
         [1913 Webster]

WordNet (r) 3.0 (2006):

descant
    n 1: a decorative musical accompaniment (often improvised) added
         above a basic melody [syn: descant, discant]
    v 1: sing in descant
    2: sing by changing register; sing by yodeling; "The Austrians
       were yodeling in the mountains" [syn: yodel, warble,
       descant]
    3: talk at great length about something of one's interest

Moby Thesaurus II by Grady Ward, 1.0:

196 Moby Thesaurus words for "descant":
   Nachtmusik, Vorspiel, absolute music, accompaniment, adaptation,
   air, air varie, aleatory, aleatory music, alto, amplify, anthem,
   aria, arrangement, article, ballad, baritone, bass, basso continuo,
   basso ostinato, bassus, canto, cantus, cantus figuratus,
   cantus planus, carol, causerie, chamber music, chamber orchestra,
   chant, chirp, chirrup, choir, chorus, comment upon, composition,
   concert overture, continuo, contralto, criticize, croon,
   curtain raiser, deal with, detail, develop, diapason, dilate,
   discourse, discuss, discussion, disquisition, dissert, dissertate,
   dissertation, ditty, do-re-mi, dramatic overture, drone, elaborate,
   electronic music, enlarge, enlarge upon, essay, etude, evolve,
   examination, excursus, exercise, expand, expatiate, explicate,
   exposition, feature, figured bass, first approach, go into,
   ground bass, handle, harmonization, homily, hum, hymn,
   incidental music, inquire into, instrumental music, intonate,
   intone, introduction, introductory study, invention, lay, lied,
   lilt, line, lucubration, measure, melodia, melodic line, melody,
   memoir, minstrel, monograph, morceau, nocturne, note,
   operatic overture, opus, orchestration, outline, overture, pandect,
   paper, paragraph, part, particularize, piece, pipe, plain chant,
   plain song, preliminary study, prelude, prick song, production,
   program music, prolegomenon, psalm, quaver, refrain,
   rehearse in extenso, relate at large, remark upon, research paper,
   review, ricercar, roulade, score, screed, serenade, sermonize,
   shake, sing, sing in chorus, sketch, sol-fa, solmizate, solo,
   solo part, sonata, sonatina, song, soprano, soprano part,
   special article, strain, string orchestra, string quartet, study,
   survey, take up, tenor, term paper, theme, theme and variations,
   thesis, thorough bass, touch upon, tract, tractate, treat,
   treat of, treatise, treatment, treble, tremolo, trill, trio, troll,
   tune, tweedle, tweedledee, twit, twitter, undersong, unfold, vamp,
   variation, vocalize, voice, voice part, voluntary, warble, whistle,
   work, work out, write up, yodel