accident vs casualty

accident and casualty both are nouns.

Word	Noun	Adjective	Verb	Adverb
accident	Yes	No	No	No
casualty	Yes	No	No	No

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

Other hyponyms of accident include collision, crash, wreck, accidental injury, injury, shipwreck, wreck, fatal accident.

accident (noun)	casualty (noun)
anything that happens suddenly or by chance without an apparent cause	a decrease of military personnel or equipment
an unfortunate mishap; especially one causing damage or injury	an accident that causes someone to die
	someone injured or killed in an accident
	someone injured or killed or captured or missing in a military engagement