an amount of money that you win or receive from someone unexpectedly意外之财
Investors each received a windfall of £3,000.投资者每人都获得了3000英镑的意外之财。
UKThe government is hoping to collect a windfall tax(= extra tax on a large unexpected company profit) from British Electric.政府打算针对英国电气公司获得的大笔意外利润征收额外的税款。