improbability vs reliability

improbability

noun
  • The quality or state of being improbable; unlikelihood. 

  • That which is improbable; an improbable event or result. 

reliability

noun
  • The quality of being reliable, dependable, or trustworthy. 

  • the ability to measure the same thing consistently (of a measurement indicating the degree to which the measure is consistent); that is, repeated measurements would give the same result (See also validity). 

  • measurable time of work before failure 

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