hickwall vs yarrow

hickwall

noun

  • A European green woodpecker, Picus viridis. 

  • A lesser spotted woodpecker, Dryobates minor. 

yarrow

noun

  • The green woodpecker, Picus viridis. 

  • Common yarrow, Achillea millefolium, the type species of the genus. 

  • Any of several pungent Eurasian and North American herbs, of the genus Achillea, used in traditional herbal medicine. 

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