act of God vs catastrophe

act of God and catastrophe both are nouns.

Word	Noun	Adjective	Verb	Adverb
act of God	Yes	No	No	No
catastrophe	Yes	No	No	No

As nouns, catastrophe is a hypernym of act of God; that is, catastrophe is a word with a broader meaning than act of God:

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

Other hypernyms of act of God include calamity, cataclysm, disaster, tragedy.

act of God (noun)	catastrophe (noun)
a natural and unavoidable catastrophe that interrupts the expected course of events	an event resulting in great loss and misfortune
	a sudden violent change in the earth's surface
	a state of extreme (usually irremediable) ruin and misfortune