farthing vs plug nickel

farthing

noun
  • A very small quantity or value; the least possible amount. 

  • Former British unit of currency worth one-quarter of an old penny; or a coin representing this. 

plug nickel

noun
  • A nearly worthless amount. 

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