unavoidable casualty vs inevitable accident

unavoidable casualty and inevitable accident both are nouns.

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

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

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

Other synonyms of unavoidable casualty include act of God, force majeure, vis major.

unavoidable casualty (noun)	inevitable accident (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