freelance vs knuckle down

freelance

verb
  • To work as a freelance. 

  • To produce or sell services as a freelance. 

noun
  • A medieval mercenary. 

  • Someone who sells their services to clients without a long-term employment contract. 

adj
  • Of, or relating to a freelance; without employment contract. 

knuckle down

verb
  • To submit; knuckle under. 

  • To get to work; to focus on a task. 

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