From meta (change) and strephō (to turn). To turn around, to change into something else, to pervert. Used of cosmic signs and the perversion of the gospel.
Peter quotes Joel's prophecy that the sun will be turned to darkness and the moon to blood before the great day of the Lord (Acts 2:20). Paul warns the Galatians about those who would pervert the gospel of Christ (Galatians 1:7). This word carries a sense of radical reversal — something being changed into its opposite. It warns against any alteration of the gospel message.