inevitable accident vs unavoidable casualty

inevitable accident and unavoidable casualty both are nouns.

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

As nouns, inevitable accident and unavoidable casualty are synonyms defined as:

inevitable accident and unavoidable casualty: a natural and unavoidable catastrophe that interrupts the expected course of events

Other synonyms of inevitable accident include act of God, force majeure, vis major.

inevitable accident (noun)	unavoidable casualty (noun)
a natural and unavoidable catastrophe that interrupts the expected course of events	a natural and unavoidable catastrophe that interrupts the expected course of events