sloe vs swarthaak

sloe

noun
  • The tree Prunus spinosa. 

  • The small, astringent, wild fruit of the blackthorn (Prunus spinosa). 

  • Any of various other plants of the genus Prunus, as a shrub or small tree, Prunus alleghaniensis, bearing dark-purple fruit. 

swarthaak

noun
  • An African thorn tree, Senegalia mellifera. 

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