Definitions for act of god
Random House Webster's College Dictionary
act′ of God′(n.)
a sudden action of natural forces that could not have been prevented, as an earthquake or hurricane.
Origin of act of God:
act of God, force majeure, vis major, inevitable accident, unavoidable casualty(noun)
a natural and unavoidable catastrophe that interrupts the expected course of events
"he discovered that his house was not insured against acts of God"
act of God(Noun)
an unforeseen occurrence beyond one's control, such as a natural disaster