pavee vs trekker

pavee

noun
  • A traveller, a member of Ireland's nomadic ethnic minority. 

trekker

noun
  • One who treks; a hiker. 

  • A person who spent the night in a rural area, rather than his home, during bombing raids. 

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