obligation vs debt instrument

obligation and debt instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
obligation	Yes	No	No	No
debt instrument	Yes	No	No	No

As nouns, obligation and debt instrument are synonyms defined as:

Other synonyms of obligation include certificate of indebtedness.

obligation (noun)	debt instrument (noun)
the social force that binds you to the courses of action demanded by that force	a written promise to repay a debt
a legal agreement specifying a payment or action and the penalty for failure to comply
a written promise to repay a debt
a personal relation in which one is indebted for a service or favor
the state of being obligated to do or pay something