propel vs tug

propel

verb
  • To provide an impetus for motion or physical action, to cause to move in a certain direction; to drive forward. 

  • To provide an impetus for non-physical change, to make to arrive to a certain situation or result. 

tug

verb
  • To pull or drag with great effort. 

  • To masturbate. 

  • To tow by tugboat. 

  • To pull hard repeatedly. 

noun
  • A dog toy consisting of a rope, often with a knot in it. 

  • A trace, or drawing strap, of a harness. 

  • A tugboat. 

  • An iron hook of a hoisting tub, to which a tackle is affixed. 

  • A sudden powerful pull. 

  • An act of male masturbation. 

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