straying from the truth: the wrong road a person ends up on, and the misleading that puts them there
Underneath this word is a picture of travel gone wrong. In ordinary Greek it named a wandering or a roaming about, the state of someone who is no longer on the road they meant to be on. Every New Testament use keeps that picture but moves it onto moral and religious ground: the road in question is the one that leads to God, and to be off it is not a small thing. James can speak of turning a sinner back from the wandering of his way and so saving a soul from death.
The word looks in two directions at once, and English cannot follow it. It can name what has happened to someone, that they are astray, and it can name what someone is doing to others, that they are pulling them off course. Our language needs "error" for the first and "deception" or "fraud" for the second, but the Greek holds both, because they are one road seen from either end. Which end is in view has to be judged from the sentence, and several verses are argued over for exactly that reason. The related verb πλανάω has the same double reach, and the person who does the leading astray gets his own word (πλάνος), which is what the chief priests call Jesus in the verse just before they call the resurrection report a fraud.
So across the New Testament the word takes three shapes:
- the wrong road a person is already walking
- a deliberate work of misleading other people
- a whole power at work against the truth
That third shape is the most striking. In 1 John it stands opposite the truth as a rival spirit, and in 2 Thessalonians it is a force let loose on people who have refused to love the truth. There the word is close to naming one side of a conflict rather than one person's mistake, and it stands against ἀλήθεια the way darkness stands against light.