castoff vs omission

castoff

noun
  • Something that has been rejected or discarded; a reject. 

adj
  • discarded, rejected. 

omission

noun
  • The act of omitting. 

  • Something not done or neglected. 

  • The shortening of a word or phrase, using an apostrophe ( ' ) to replace the missing letters, often used to approximate the sound of speech or a specific dialect. 

  • An instance of those acts, or the thing left out thereby; something deleted or left out. 

  • The act of neglecting to perform an action one has an obligation to do. 

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