middle finger vs trigger finger

middle finger

noun
  • The finger between the forefinger and the ring finger 

  • An obscene gesture directed towards another as an insult, made by sticking up the middle finger of a hand. 

  • An insult directed at someone. 

trigger finger

noun
  • the forefinger 

  • a finger used in pulling the trigger of a firearm 

  • difficulty encountered in finger flexion or extension caused by the narrowing of the sheath that surrounds that finger's tendon 

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