What is the difference between being a...

The original meanings of these words were that a citizen was a natural-born resident of a locale, and a denizen was an alien who was made into a citizen through some process. Under these definitions, it could be said that new immigrants to the United States became denizens when they became naturalized citizens. The word denizen comes from the Latin term de-intus, meaning “from within,” and is most often used today to denote someone who frequents a certain place.