maternal cousin vs sibling

maternal cousin

noun
  • A child of one's mother's sibling 

  • A more distant relative of one's mother who is not a direct ancestor 

sibling

noun
  • A person who shares a parent; one's brother or sister who one shares a parent with. 

  • A node in a data structure that shares its parent with another node. 

  • The most closely related species, or one of several most closely related species when none can be determined to be more closely related. 

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