descant vs discourse

descant

noun
  • A lengthy discourse on a subject. 

  • A counterpoint melody sung or played above the theme. 

verb
  • To sing or play a descant. 

  • To discuss at length. 

discourse

noun
  • A formal lengthy exposition of some subject, either spoken or written. 

  • Expression in words, either speech or writing. 

  • An institutionalized way of thinking, a social boundary defining what can be said about a specific topic (after Michel Foucault). 

  • Any rational expression, reason. 

verb
  • To exercise reason; to employ the mind in judging and inferring; to reason. 

  • To engage in discussion or conversation; to converse. 

  • To write or speak formally and at length. 

How often have the words descant and discourse occurred in a corpus of books? (source: Google Ngram Viewer )