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.
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.