obligation vs CD

obligation and CD both are nouns.

Word	Noun	Adjective	Verb	Adverb
obligation	Yes	No	No	No
CD	Yes	No	No	No

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

obligation (noun)	CD (noun)
the social force that binds you to the courses of action demanded by that force	a digitally encoded recording on an optical disk that is smaller than a phonograph record; played back by a laser
a legal agreement specifying a payment or action and the penalty for failure to comply	a debt instrument issued by a bank; usually pays interest
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