conch vs plastron

conch

noun
  • The shell of this sea animal. 

  • A marine gastropod of the family Strombidae which lives in its own spiral shell. 

  • A musical instrument made from a large spiral seashell, somewhat like a trumpet. 

  • Synonym of concher (“machine used to refine the flavour and texture of chocolate”) 

  • The semidome of an apse, or the apse itself. 

verb
  • To refine the flavour and texture of chocolate by warming and grinding, either in a traditional concher, or between rollers. 

  • To play a conch seashell as a musical instrument, by blowing through a hole made close to the origin of the spiral. 

plastron

noun
  • The nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace. 

  • A breastplate. 

  • A half-jacket worn under the jacket for padding or for safety. 

  • A film of air trapped by specialized hairs against the body of an aquatic insect, and which acts as an external gill. 

  • An ornamental front panel on a woman's bodice. 

  • A man's shirt-bosom. 

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