Whoa (interjection)

1. Used to express surprise, amazement, or to get someone's attention.
2. Used to express a desire to slow down or stop.

Origin:

Probably an alteration of ho, a command to horses.

Examples:

1. Whoa, did you see that? That was amazing!
2. Whoa there, slow down. I can't keep up!
3. Whoa, what happened? Did someone get hurt?
4. Whoa, that was a close call.
5. Whoa, did you see how high that building is?