post-obit vs posthumous

post-obit

noun
  • A bond in which the obligor, in consideration of having received a certain sum of money, binds himself to pay a larger sum, on unusual interest, on the death of some specified individual from whom he has expectations. 

posthumous

adj
  • In reference to a work, published after the author's death. 

  • Taking place after one's own death. 

  • Born after the death of one's father. 

  • After the death of someone. 

How often have the words post-obit and posthumous occurred in a corpus of books? (source: Google Ngram Viewer )