Attestant and Testifier

Attestant noun - Someone who affirms or vouches for the correctness or truth or genuineness of something.

Testifier and attestant are semantically related in witness topic. In some cases you can use "Testifier" instead a noun "Attestant", when it comes to topics like person who observes an event.

Testifier noun - A person who testifies or gives a deposition.

Attestant and testifier are semantically related in witness topic. You can use "Attestant" instead a noun "Testifier", if it concerns topics such as law.