attestor vs signer

attestor and signer both are nouns.

Word	Noun	Adjective	Verb	Adverb
attestor	Yes	No	No	No
signer	Yes	No	No	No

As nouns, signer is a hypernym of attestor; that is, signer is a word with a broader meaning than attestor:

attestor: (law) a person who attests to the genuineness of a document or signature by adding their own signature
signer: someone who signs and is bound by a document

Other hypernyms of attestor include signatory.

attestor (noun)	signer (noun)
(law) a person who attests to the genuineness of a document or signature by adding their own signature	someone who signs and is bound by a document
	someone who can use sign language to communicate