gradual vs subitaneous

gradual

adj
  • Proceeding or advancing by small, slow, regular steps or degrees 

noun
  • A service book containing the musical portions of the Mass. 

  • An antiphon or responsory after the epistle, in the Mass, which was sung on the steps, or while the deacon ascended the steps. 

subitaneous

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