debt instrument vs obligation

debt instrument and obligation both are nouns.

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

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

Other synonyms of debt instrument include certificate of indebtedness.

debt instrument (noun)	obligation (noun)
a written promise to repay a debt	the social force that binds you to the courses of action demanded by that force
	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