serendipity vs good fortune

serendipity and good fortune both are nouns.

Word	Noun	Adjective	Verb	Adverb
serendipity	Yes	No	No	No
good fortune	Yes	No	No	No

As nouns, good fortune is a hypernym of serendipity; that is, good fortune is a word with a broader meaning than serendipity:

Other hypernyms of serendipity include fluke, good luck.

serendipity (noun)	good fortune (noun)
good luck in making unexpected and fortunate discoveries	a stroke of luck
	an auspicious state resulting from favorable outcomes