crocus vs yolk

crocus

noun
  • Burlap. 

  • A perennial flowering plant (of the genus Crocus in the Iridaceae family). Saffron is obtained from the stamens of Crocus sativus. 

  • Any of various similar flowering plants, such as the autumn crocus and prairie crocus. 

yolk

noun
  • The grease in a sheep's fleece; lanolin. 

  • The yellow, spherical part of an egg that is surrounded by the white albumen, and serves as nutriment for the growing young. 

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