plod vs toil

plod

verb
  • To toil; to drudge; especially, to study laboriously and patiently. 

  • To walk or move slowly and heavily or laboriously (+ on, through, over). 

  • To trudge over or through. 

noun
  • A slow or labored walk or other motion or activity. 

  • the police, police officers 

  • a police officer, especially a low-ranking one. 

toil

verb
  • To work (something); often with out. 

  • To struggle. 

  • To labour; work. 

  • To weary through excessive labour. 

noun
  • Trouble, strife. 

  • Labour, work, especially of a grueling nature. 

  • A net or snare; any thread, web, or string spread for taking prey. 

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