mother-of-pearl vs sheath

mother-of-pearl

noun
  • A butterfly of the genus Salamis. 

  • The hard pearly inner layer of certain mollusk shells; nacre. 

adj
  • Made from or looking like mother-of-pearl; iridescent or pearly. 

sheath

noun
  • One of the elytra of an insect. 

  • The base of a leaf when sheathing or investing a branch or stem, as in grasses. 

  • A holster for a sword; a scabbard. 

  • A condom. 

  • The foreskin of certain animals (for example, dogs and horses). 

  • A tight-fitting dress. 

  • Anything that has a similar shape to a scabbard that is used to hold an object that is longer than it is wide. 

  • The insulating outer cover of an electrical cable. 

How often have the words mother-of-pearl and sheath occurred in a corpus of books? (source: Google Ngram Viewer )