polychromasia vs undertone

polychromasia

noun
  • A disorder in which there is an abnormally high number of red blood cells in the bloodstream as a result of their having been prematurely released from the bone marrow during blood formation. 

undertone

verb
  • To accompany as an undertone. 

  • To say or speak in an undertone. 

  • To present as less important, noticeable or prominent. 

noun
  • A pale colour, or one seen underneath another colour. 

  • A low state of the physical faculties. 

  • An implicit message perceived subtly alongside, but not detracting noticeably from, the explicit message conveyed in or by a book, film, verbal dialogue or similar (contrast with overtone); an undercurrent. 

  • An auditory tone of low pitch or volume. 

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