constantly vs oftentimes

constantly

adv
  • Recurring regularly. 

  • In an unchangeable or invariable manner; in every case. 

  • In a constant manner; occurring continuously; persistently. 

oftentimes

adv
  • (elsewhere, archaic) Frequently; often 

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