cubit vs fuck finger

cubit

noun
  • The distance from the elbow to the tip of the middle finger used as an informal unit of length. 

  • Any of various units of length approximating this distance, usually around 35–60 cm. 

fuck finger

noun
  • The middle finger 

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