haystack vs undulation

haystack

noun
  • A standing wave in a rapid. 

  • A dish composed of a starchy food (rice, tortillas, crackers, etc.) topped by a protein (beans, cheese, meat, etc.) in combination with fresh vegetables, assembled on the plate by the diner. 

  • A mound, pile, or stack of stored hay. 

  • The text string within which another string is searched for. (see: needle in a haystack) 

undulation

noun
  • A wavelike curve; a smooth and regular rise and fall. 

  • An instance or act of undulating. 

  • A wavy appearance or outline; waviness. 

  • A wavelike motion of the air; electromagnetic radiation. 

  • A tremulous tone produced by a peculiar pressure of the finger on a string. 

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