Definition: Demetrius is a Greek god associated with love, youthfulness, and youthful excesses. It's also used as an adjective to describe someone who appears young or immature. The word means "young" in Latin and is derived from "demitra," which means "young." In the context of the word, it can mean being not fully grown yet but just getting started in life. For example, he was a demetrius when he was 18 years old.