happy chance vs chance event

happy chance and chance event both are nouns.

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

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

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

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

happy chance (noun)	chance event (noun)
an unexpected piece of good luck	anything that happens suddenly or by chance without an apparent cause