portent vs prelude

portent

noun
  • Something regarded as portentous; a marvel; prodigy. 

  • A portending; significance 

  • Something that portends an event about to occur, especially an unfortunate or evil event; an omen. 

prelude

noun
  • A forerunner to anything. 

  • An introductory or preliminary performance or event. 

  • A standard module or library of subroutines and functions to be imported, generally by default, into a program. 

  • A short, free-form piece of music, originally one serving as an introduction to a longer and more complex piece; later, starting with the Romantic period, generally a stand-alone piece. 

verb
  • To play an introduction or prelude; to give a prefatory performance. 

  • To introduce something, as a prelude. 

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