indubious vs probable

indubious

adj
  • Not dubious or doubtful; certain. 

  • Not doubting; unsuspecting. 

probable

adj
  • Likely or most likely to be true. 

  • Supporting, or giving ground for, belief, but not demonstrating. 

  • Likely to happen. 

noun
  • A person who is likely to appear or do a certain thing. 

  • Something that is likely. 

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