separate vs sign on

separate

verb
  • To disunite from a group or mass; to disconnect. 

  • To divide (a thing) into separate parts. 

  • To cause (things or people) to be separate. 

  • To divide itself into separate pieces or substances. 

adj
  • Apart from (the rest); not connected to or attached to (anything else). 

  • Not together (with); not united (to). 

noun
  • A printing of an article from a periodical as its own distinct publication and distributed independently, often with different page numbers. 

  • Anything that is sold by itself, especially articles of clothing such as blouses, skirts, jackets, and pants. 

sign on

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. 

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

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