increditable vs lackluster

increditable

adj
  • Incapable of being believed; not creditable. 

lackluster

adj
  • Not exceptional; not worthy of special merit, attention, or interest; having no vitality. 

  • Having no shine or lustre; dull. 

  • Lacking brilliance or intelligence. 

noun
  • Lack of brightness or points of interest. 

  • A person or thing of no particular brilliance or intelligence. 

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