fortune vs toss-up

fortune and toss-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
fortune	Yes	No	No	No
toss-up	Yes	No	No	No

As nouns, toss-up is a hyponym of fortune; that is, toss-up is a word with a more specific, narrower meaning than fortune:

fortune: an unknown and unpredictable phenomenon that causes an event to result one way rather than another
toss-up: an unpredictable phenomenon

Other hyponyms of fortune include bad luck, mischance, mishap, even chance, tossup.

fortune (noun)	toss-up (noun)
an unknown and unpredictable phenomenon that causes an event to result one way rather than another	an unpredictable phenomenon
an unknown and unpredictable phenomenon that leads to a favorable outcome
a large amount of wealth or prosperity
your overall circumstances or condition in life (including everything that happens to you)