gratis vs gratuitously

gratis

adv
  • Free, without charge. 

adj
  • Free, without charge. 

gratuitously

adv
  • Freely; in the manner of a gift, without being earned. 

  • In a manner not demanded by the circumstances, without reason, justification, cause, or proof. 

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