Satanas in Latinum sonat adversarius, sive transgressor. ipse est enim adversarius, qui est veritatis inimicus, et semper sanctorum virtutibus contraire nititur. ipse et transgressor, quia praevaricator effectus in veritate, qua conditus est, non stetit. idem et temptator, quia temptandam iustorum innocentiam postulat, sicut in libro Iob scribitur. Antichristus appellatur, quia contra Christum venturus est, non, quomodo quidem simplices intellegunt, Antichristum ideo dictum, quod ante Christum venturus sit, id est post eum veniet Christus. non sic, sed Antichristus Graece dicitur, quod est Latine contrarius Christo. ἀντὶ enim Graece in Latinum ‘contra’ significat. Christum enim se mentietur, cum venerit, et contra eum dimicabit, et adversabitur sacramentis Christi, ut veritatis eius evangelium solvat. nam et templum Hierosolymis reparare, et omnes veteris legis ceremonias restaurare temptabit. sed et ille Antichristus est, qui negat esse Dominum Christum. contrarius est enim Christo. omnes enim, qui exeunt de ecclesia et ab unitate fidei praeciduntur, et ipsi Antichristi sunt.
(Isidorus of Sevilla, Etym. 11.1.99-101)
Satan (Satanas) means “adversary,” or “transgressor” in Latin. He is indeed the adversary who is the enemy of truth, and he always strives to go against the virtues of the holy. He is also the transgressor, because as a complete prevaricator, he did not continue in the truth in which he was created. Also he is the tempter, because he claims that the innocence of the righteous must be tempted, as it is written in Job. He is called the Antichrist (Antichristus), because he is to come against Christ. He is not, as certain simpletons suppose, called the Antichrist because he is to come before (ante) Christ, that is, that Christ would come after him. This is not the case, but rather he is called Antichrist in Greek, which is ‘against Christ’ (contrarius Christo) in Latin, for ἀντί in Greek means ‘against’ in Latin. When he comes he will pretend that he is Christ, and there will be a struggle against him, and he will oppose the sacraments of Christ in order to destroy the gospel of his truth. For he will attempt to rebuild the temple at Jerusalem and restore all the rites of the old Law. But Antichrist is also one who denies that Christ is God, for he is the opposite of Christ. So all those who depart from the Church and are cut off from the unity of faith are themselves Antichrists. (tr. Stephen A. Barney, W.J. Lewis, J.A. Beach and/or Oliver Berghof)