inevitable accident vs calamity

inevitable accident and calamity both are nouns.

Word	Noun	Adjective	Verb	Adverb
inevitable accident	Yes	No	No	No
calamity	Yes	No	No	No

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

inevitable accident: a natural and unavoidable catastrophe that interrupts the expected course of events
calamity: an event resulting in great loss and misfortune

Other hypernyms of inevitable accident include cataclysm, catastrophe, disaster, tragedy.

inevitable accident (noun)	calamity (noun)
a natural and unavoidable catastrophe that interrupts the expected course of events	an event resulting in great loss and misfortune