fort vs weak point

fort

verb
  • To create a fort, fortifications, a strong point, or a redoubt. 

noun
  • Any permanent army post. 

  • An outlying trading-station, as in British North America. 

  • A structure improvised from furniture, bedding, etc., for playing games. 

  • A fortified defensive structure stationed with troops. 

weak point

noun
  • Something at which someone, or something, is substandard 

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