cohabit vs get it on

cohabit

verb
  • To live together with someone else, especially in a romantic and sexual relationship but without being married. 

  • To coexist in common environs with. 

get it on

verb
  • To have sex. 

  • To engage in a fight. 

  • To hurry up; to get a move on. 

  • Used other than figuratively or idiomatically: see get, it, on. 

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