breath vs undertone

breath

noun
  • The act or process of breathing. 

  • A single act of breathing in or out; a breathing of air. 

  • Air expelled from the lungs. 

  • A rest or pause. 

  • A small amount of something, such as wind, or common sense. 

adj
  • voiceless, surd; contrasting with voice (breath sounds, voice sounds) 

undertone

noun
  • An auditory tone of low pitch or volume. 

  • 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. 

verb
  • To accompany as an undertone. 

  • To say or speak in an undertone. 

  • To present as less important, noticeable or prominent. 

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