casualty vs accident

casualty and accident both are nouns.

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

As nouns, accident is a hypernym of casualty; that is, accident is a word with a broader meaning than casualty:

Other hypernyms of casualty include fatality, human death.

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