custodian vs libero

custodian

noun
  • a janitor; a cleaner 

  • A person entrusted with the custody or care of something or someone; a caretaker or keeper. 

libero

noun
  • a sweeper 

  • a designated back-row player intended to be used as a ball-control specialist 

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