The Hebrew “Satan,” which appears in the Old Testament as the name of the enemy of mankind, means literally “adversary.”
When the Old Testament was rendered into Greek the translators looked for a word to reproduce this literal meaning.
They hit upon diabolos, the noun from diaballein, which was compounded of dia, across, and ballein, to throw. Diaballein, from meaning “to throw across,” had come to mean “to slander or accuse”; and diabolos, therefore, meant “accuser.”
Accordingly, the Devil, whose name is derived from diabolos, is properly to be regarded as the accuser of the soul.