Windfall' (3 letters) A big WINDFALL is a large, unexpected gain or benefit. It can be used to describe a sudden influx of money, resources, or luck. The term 'big WINDFALL' can be broken down into two words: 'BONANZA' (7 letters) and 'WINDFALL' (3 letters). A BONANZA is a large amount of something valuable, while a WINDFALL is an unexpected gain or benefit. Together, these two words form the phrase 'big WINDFALL, ' which describes a large, unexpected gain or benefit.