This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. a person who attests to the genuineness of a document or signature by adding their own signature.

Bearing witness

n. An attesting witness: an attester.

n. (law) a person who attests to the genuineness of a document or signature by adding their own signature

n. someone who affirms or vouches for the correctness or truth or genuineness of something

"Mesothelioma prognosis gravely agonistic patients hawthorn attestant inspiratory crackles and clubbing of fingers."

signer    signatory    witnesser    witness    informant   

witness