happy chance vs accident

happy chance and accident both are nouns.

Word	Noun	Adjective	Verb	Adverb
happy chance	Yes	No	No	No
accident	Yes	No	No	No

As nouns, accident is a hypernym of happy chance; that is, accident is a word with a broader meaning than happy chance:

happy chance: an unexpected piece of good luck
accident: anything that happens suddenly or by chance without an apparent cause

Other hypernyms of happy chance include chance event, fortuity, stroke.

happy chance (noun)	accident (noun)
an unexpected piece of good luck	anything that happens suddenly or by chance without an apparent cause
	an unfortunate mishap; especially one causing damage or injury