heliotrope vs purple dye murex

heliotrope

noun
  • A light purple or violet colour. 

  • Particularly, a purple-flowered plant of the species Heliotropium arborescens. 

  • A bloodstone (a variety of quartz). 

  • An instrument, employed in triangulation, that uses a mirror to reflect sunlight toward another, very distant, surveyor. 

  • The fragrance of heliotrope flowers. 

  • A plant that turns so that it faces the sun. 

adj
  • Light purple or violet. 

  • Keeping one’s face turned toward the sun. 

purple dye murex

noun
  • A species of medium-sized predatory sea snail, Haustellum brandaris, which secrets a substance that can be used to make a long-lasting purple dye- Tyrian purple. 

How often have the words heliotrope and purple dye murex occurred in a corpus of books? (source: Google Ngram Viewer )