memory hole vs memory-hole

memory hole

noun
  • A memory leak. 

  • A figurative place to which lost or forgotten information is sent, usually deliberately; nowhere. 

  • A fragment of physical address space which does not map to main memory. 

memory-hole

verb
  • To cause something or someone to be forgotten. 

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