From Longman Dictionary of Contemporary Englishwindfall taxˈwindfall ˌtax noun [countable] an additional amount of tax that the British government sometimes takes from a company that has suddenly earned a large amount of money that it did not expect to earn
Examples from the Corpus
windfall tax• Labour has imposed the utility windfall tax, introduced the minimum wage and ramped up petrol duty.From Longman Business Dictionarywindfall taxˈwindfall tax [countable]TAX a tax that must be paid by a company that has suddenly and unexpectedly earned a large amount of money, especially a large company that has recently been PRIVATIZED (=sold by the government) → tax 