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]