hazard vs toss-up

hazard and toss-up both are nouns.

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

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

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

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

hazard (noun)	toss-up (noun)
an obstacle on a golf course	an unpredictable phenomenon
an unknown and unpredictable phenomenon that causes an event to result one way rather than another
a source of danger; a possibility of incurring loss or misfortune

hazard (verb)	toss-up (verb)
put forward, of a guess, in spite of possible refutation
take a risk in the hope of a favorable outcome
put at risk