verge
The point when something is just about to happen.
When you're on the verge of something, you're right at the edge of it, about to cross over into it happening. A student on the verge of tears is holding them back but barely. A scientist on the verge of a breakthrough is so close to solving the problem that it could happen any moment.
The word captures that tense moment right before something changes. You might be on the verge of laughing during a serious assembly, fighting to keep your face straight. A team on the verge of victory leads by one point with seconds left on the clock. The word often appears with “on the”: on the verge of sleep, on the verge of giving up, on the verge of understanding a difficult concept.
Think of standing at the very edge of a diving board, toes curled over the end, about to jump. That's the feeling of being on the verge: the decision or change is so close you can almost feel it, but it hasn't quite happened yet.