The most common English synonym for “Satan” is “devil”, which descends from Middle English devel, from Old English dēofol, that in turn represents an early Germanic borrowing of Latin diabolus (also the source of “diabolical”). This in turn was borrowed from Greek diabolos “slanderer”, from diaballein “to slander”: dia- “across, through” + ballein “to hurl”.
In many cases, the translators of the Septuagint, the pre-Christian translation of the Hebrew Bible into ancient Greek, chose to render the Hebrew word sâtan as the Greek word διάβολος (diábolos), meaning “opponent” or “accuser”. This is the root of the modern English word Devil. Both the words satanas and diábolos are used interchangeably in the New Testament and in later Christian writings.