cowberry vs twinberry

cowberry

noun
  • The berry of this shrub. 

  • A shrub native to the cool temperate areas of the Northern Hemisphere (Vaccinium vitis-idaea). 

twinberry

noun
  • Its fruit, a bitter edible black berry containing several small seeds. 

  • A North American species of honeysuckle, Lonicera involucrata. 

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