first finger vs thumby

first finger

noun

  • thumb 

  • index finger 

thumby

noun

  • A little thumb; diminutive term for thumb 

adj

  • Clumsy, awkward, maladroit, not dextrous, all thumbs 

  • Dirtied by thumb marks 

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