eidō

This is the ordinary New Testament word for seeing something happen and grasping what it means. In practice it almost always appears in its past-tense form ("saw"), and it is the verb the Gospels reach for again and again: someone sees a crowd, sees a sick person, sees Jesus, and acts on what they have seen.

The word travels naturally from the eye to the mind. To see a thing is often, in the same breath, to take in what it signifies, so "he saw" frequently shades into "he perceived" or "he realized." When Jesus "saw" people's thoughts or someone "saw" that an answer was wise, nothing physical is in view at all; the word has moved fully into the sense of understanding a situation.

It also covers seeing in the sense of going to look, visiting, or witnessing an event, and in the book of Revelation it is the steady drumbeat that introduces each new vision: "I saw." One short command form of it, often printed as "Behold!" or "Look!", is really just "see this" used to point.

Greek built this meaning on a striking idea: to have seen something is to know it. So the verb has a second life as the common word for settled, sure knowledge. In form it looks like a past tense ("had seen"), but it is used with present force, "I know," because the knowing is the lasting result of having taken something in.

It covers knowing a fact ("he knew that they had handed him over out of envy"), knowing or recognizing a person ("the disciples did not know it was Jesus"), and knowing what to do or say in a moment (the frightened disciples "did not know what to answer"). Across all of these the common thread is assured, in-hand knowledge rather than the process of coming to learn.

This is what sets it apart from its close neighbor, the verb that means to get to know, to learn, or to come to recognize something over time. That word watches knowledge being gained; this one names knowledge already possessed. English blurs them into the one word "know," but the New Testament writers, especially John, often play the two off each other on purpose.