Initially, the word satan was a Hebrew common noun meaning “adversary” or “opponent.” The word was used to refer to human adversaries. In time, satan came to mean a supernatural opponent, a messenger sent by God for the specific purpose of blocking or obstructing human activity, like the angel in the story of Balaam:
And Balaam rose up in the morning, and saddled his ass, and went with the princes of Moab. And God’s anger was kindled because he went: and the angel of the LORD stood in the way for an adversary against him. –Numbers 22:21-22
In the Book of Job, Satan is the name of a member of God’s court:
Now there was a day when the sons of God came to present themselves before the Lord, and Satan came also among them. –Job 1:6
The name Satan eventually came to be the proper name of the personification of evil. When the Hebrew Bible was translated into Greek, the word “satan” was translated as diabolus, the Greek word for “adversary.” Diabolus became diavolo in Italian, diable in French, diablo in Spanish, Teufel in German, and devil in English. As a common noun, devil refers to an agent of evil, either human or supernatural. As a proper noun with the definite article, the Devil refers to the chief “devil,” Satan.