doubtful vs subnormal

doubtful

noun
  • A doubtful person or thing. 

adj
  • Experiencing or showing doubt, sceptical. 

  • Subject to, or causing doubt. 

  • Improbable or unlikely. 

  • Unclear or unreliable. 

  • Suspicious, or of dubious character. 

  • Undecided or of uncertain outcome. 

subnormal

noun
  • A person whose abilities are less than normal. 

  • That part of the axis of a curved line which is intercepted between the ordinate and the normal. 

adj
  • denormal 

  • Less than normal. 

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