dullen vs prose

dullen

verb
  • To make dull or duller; to dull. 

  • To become dull or duller; to dull. 

prose

verb
  • To write or repeat in a dull, tedious, or prosy way. 

noun
  • Language, particularly written language, not intended as poetry. 

  • Language which evinces little imagination or animation; dull and commonplace discourse. 

  • A hymn with no regular meter, sometimes introduced into the Mass. 

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