thwart vs ward off

thwart

verb
  • To cause to fail; to frustrate, to prevent. 

noun
  • A seat across a boat on which a rower may sit. 

  • An act of thwarting; something which thwarts; a hindrance, an obstacle. 

  • A brace, perpendicular to the keel, that helps maintain the beam (“breadth”) of a marine vessel against external water pressure and that may serve to support the rail. 

adj
  • Placed or situated across something else; cross, oblique, transverse. 

ward off

verb
  • To avert or prevent. 

  • To parry, or turn aside. 

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