Aha (interjection)

1. Used to express sudden realization, understanding, or recognition.
2. Used to express triumph, surprise, or amusement.

Origin:

Mid 19th century: imitative.

Examples:

1. Aha! I knew I'd seen that face before!
2. Aha! So that's the secret!
3. Aha! I finally figured it out!
4. The detective said, 'Aha! I have found the culprit.'.
5. Aha! I see what you did there.