swan song vs ulterior

swan song

noun
  • A final performance or accomplishment, especially one before retirement. 

ulterior

adj
  • Being intentionally concealed so as to deceive. 

  • Situated beyond, or on the farther side. 

  • Beyond what is obvious or evident. 

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