such-and-such vs unapprehended

such-and-such

noun

  • A placeholder or generic thing. 

det

  • indefinite; some or other, not stated 

unapprehended

adj

  • Not apprehended. 

  • Not understood. 

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