enroll vs take on

enroll

verb
  • To enlist oneself (in something) or become a member (of something) 

  • To enter (a name, etc.) in a register, roll or list 

  • To enlist (someone) or make (someone) a member of 

take on

verb
  • To acquire, bring in, or introduce. 

  • To assume or take responsibility for. 

  • To (attempt to) dribble round (an opposition player). 

  • To catch on, do well; to become popular. 

  • To obtain the services of (a person) in exchange for remuneration; to give someone a job. 

  • To begin to have or exhibit. 

  • To attempt to fight, compete with, or engage with. 

  • To grieve or be concerned (about something or someone). 

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