imbecility vs thoughtlessness

imbecility

noun
  • Something imbecilic; a stupid action, behaviour, etc. 

  • The quality of being imbecile; weakness; feebleness, especially of mind. 

thoughtlessness

noun
  • heedless disregard for the consequences of one's actions 

  • disregard for other's feelings 

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