0 to accept that an amount of money has been lost or that a debt will not be paid: --
1 to damage a vehicle so badly that it cannot be repaired: --
His car was completely written off in the accident.
2 to accept that an amount of money has been lost, for example, from a bad investment or a debt that will never be paid, and show it as a loss in a company's accounts: --
Banks accept that some of their bad debts will eventually have to be written off.
3 to damage a vehicle so badly that it cannot be repaired, or it would cost too much to repair: --
The car was completely written off.