certificate of indebtedness vs debt instrument

certificate of indebtedness and debt instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
certificate of indebtedness	Yes	No	No	No
debt instrument	Yes	No	No	No

As nouns, certificate of indebtedness and debt instrument are synonyms defined as:

certificate of indebtedness and debt instrument: a written promise to repay a debt

Other synonyms of certificate of indebtedness include obligation.

certificate of indebtedness (noun)	debt instrument (noun)
a written promise to repay a debt	a written promise to repay a debt