fluke vs serendipity

fluke and serendipity both are nouns.

Word	Noun	Adjective	Verb	Adverb
fluke	Yes	No	No	No
serendipity	Yes	No	No	No

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

fluke (noun)	serendipity (noun)
parasitic flatworms having external suckers for attaching to a host	good luck in making unexpected and fortunate discoveries
either of the two lobes of the tail of a cetacean
flat bladelike projection on the arm of an anchor
a barb on a harpoon or arrow
a stroke of luck