call up vs unknow

call up

noun
  • An order to report for military service. 

verb
  • To select e.g. to a sports squad. 

  • To summon (someone) to report for military service. 

  • To retrieve from personal or computer memory. 

  • To call on the telephone. 

unknow

verb
  • To undo the process of knowing, to lose knowledge of something. 

How often have the words call up and unknow occurred in a corpus of books? (source: Google Ngram Viewer )