fortuity vs good luck

fortuity and good luck both are nouns.

Word	Noun	Adjective	Verb	Adverb
fortuity	Yes	No	No	No
good luck	Yes	No	No	No

As nouns, good luck is a hyponym of fortuity; that is, good luck is a word with a more specific, narrower meaning than fortuity:

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

Other hyponyms of fortuity include hap, break, happy chance, coincidence, happenstance, lottery.

fortuity (noun)	good luck (noun)
anything that happens suddenly or by chance without an apparent cause	an unexpected piece of good luck
	a stroke of luck
	an auspicious state resulting from favorable outcomes