enroll vs refrain

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 

refrain

noun
  • The chorus or burden of a song repeated at the end of each verse or stanza. 

  • A much repeated comment, complaint, or saying. 

verb
  • To stop oneself from some action or interference; to abstain. 

  • To abstain from (food or drink). 

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