toss-up vs luck

toss-up and luck both are nouns.

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

As nouns, luck is a hypernym of toss-up; that is, luck is a word with a broader meaning than toss-up:

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

Other hypernyms of toss-up include chance, fortune, hazard.

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