Definition
Millennian, although less common than "millennial," essentially has the same primary meaning. It primarily describes something related to a millennium, which is a period of one thousand years. More casually, it also can be used to refer to a person who was born around the turn of the millennium (around the year 2000) or who came of age around that time. It's basically a synonym for "millennial" but is less frequently used in common speech or writing.