endeavor vs one’s level best

endeavor

noun
  • A sincere attempt; a determined or assiduous effort towards a specific goal; assiduous or persistent activity. 

verb
  • To work with purpose. 

  • To attempt through application of effort (to do something); to try strenuously. 

one’s level best

How often have the words endeavor and one’s level best occurred in a corpus of books? (source: Google Ngram Viewer )