expel vs sign on

expel

verb
  • To eject or erupt. 

  • To remove from membership. 

  • To deport. 

sign on

noun
  • The time of day when a radio or television station begins broadcasting, usually after being off the air for several hours. 

verb
  • To begin broadcasting a radio or television signal, usually at the beginning of a broadcasting day and after being off the air for several hours. 

  • To commit oneself, as to a project, a goal, an organization, a cause. 

  • To join something, after signing. 

  • To apply to receive unemployment benefits. 

  • To log on; to start using a computer, radio, etc., or to start talking. 

How often have the words expel and sign on occurred in a corpus of books? (source: Google Ngram Viewer )