heliotrope vs indigo

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. 

indigo

noun
  • A purplish-blue colour 

  • An indigo-colored dye obtained from certain plants (the indigo plant or woad), or a similar synthetic dye. 

  • An indigo plant, such as from species in genera Indigofera, Amorpha (false indigo), Baptisia (wild indigo), and Psorothamnus and Dalea (indigo bush). 

adj
  • having a deep purplish-blue colour 

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