Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. To comment freely; to discourse with fullness and
      particularity; to discourse at large.

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

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.

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

                She [the nightingale] all night long her amorous
                descant sung.                     --Milton.

   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.

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

            Upon that simplest of themes how magnificent a
            descant!                              --De Quincey.

Source : WordNet®

descant
     n : a decorative musical accompaniment (often improvised) added
         above a basic melody [syn: {discant}]

descant
     v 1: sing in descant
     2: sing by changing register; sing by yodeling; "The Austrians
        were yodeling in the mountains" [syn: {yodel}, {warble}]
     3: talk at great length about something of one's interest