sperm vs yolk

sperm

noun
  • Semen; the generative substance of male animals. 

  • The reproductive cell or gamete of the male; a spermatozoon. 

  • Sperm oil; whale oil from a sperm whale; spermaceti. 

verb
  • To ejaculate on or into. 

  • To ejaculate. 

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 sperm and yolk occurred in a corpus of books? (source: Google Ngram Viewer )