(plain) vanilla vs prosaic

(plain) vanilla

prosaic

adj
  • Straightforward; matter-of-fact; lacking the feeling or elegance of poetry. 

  • Pertaining to or having the characteristics of prose. 

  • Overly plain, simple or commonplace, to the point of being boring. 

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