Good news, glad tidings. From eu (good) + angelos (messenger). In the Roman world, euangelion announced imperial victories and the emperor's birthday. The NT claimed the word for a greater announcement: God has acted in Christ to save the world.
The euangelion is not advice but news — the announcement of something that has happened. Christ died for our sins, was buried, and was raised (1 Corinthians 15:3-4). Paul stakes everything on it: 'I am not ashamed of the gospel, because it is the power of God' (Romans 1:16). Using the Roman term was subversive — the real good news is not Caesar's but Christ's. The gospel is both the message and the power it carries.