plod vs tiptoe

plod

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

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

  • 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. 

tiptoe

verb
  • To walk quietly with only the tips of the toes touching the ground. 

adj
  • Standing elevated, on or as if on the tips of one's toes. 

  • Moving carefully, quietly, warily or stealthily, on or as if on the tips of one's toes. 

noun
  • The tip of the toe. 

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