indebtedness vs arrears

indebtedness and arrears both are nouns.

Word	Noun	Adjective	Verb	Adverb
indebtedness	Yes	No	No	No
arrears	Yes	No	No	No

As nouns, arrears is a hyponym of indebtedness; that is, arrears is a word with a more specific, narrower meaning than indebtedness:

Other hyponyms of indebtedness include limited liability, debt, account payable, payable, scot and lot.

indebtedness (noun)	arrears (noun)
a personal relation in which one is indebted for a service or favor	an unpaid overdue debt
an obligation to pay money to another party	the state of being behind in payments