affidavit vs legal instrument

affidavit and legal instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
affidavit	Yes	No	No	No
legal instrument	Yes	No	No	No

As nouns, legal instrument is a hypernym of affidavit; that is, legal instrument is a word with a broader meaning than affidavit:

affidavit: written declaration made under oath; a written statement sworn to be true before someone legally authorized to administer an oath
legal instrument: (law) a document that states some contractual relationship or grants some right

Other hypernyms of affidavit include instrument, legal document, official document, testimony.

affidavit (noun)	legal instrument (noun)
written declaration made under oath; a written statement sworn to be true before someone legally authorized to administer an oath	(law) a document that states some contractual relationship or grants some right