glottis vs hiatus

glottis

noun
  • The opening between the true vocal cords which is located in the larynx and affects voice modulation through expansion or contraction. 

hiatus

noun
  • A syllable break between two vowels, without an intervening consonant. (Compare diphthong.) 

  • A gap in a series, making it incomplete. 

  • An opening in an organ. 

  • A gap in geological strata. 

  • An unexpected break from work. 

  • An interruption, break or pause. 

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