deterrent vs illusion

deterrent

adj
  • Serving to deter, preventing something from happening. 

noun
  • Something that deters. 

illusion

noun
  • A misapprehension; a belief in something that is in fact not true. 

  • Anything that seems to be something that it is not. 

  • A magician’s trick. 

  • The state of being deceived or misled. 

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