C1 noun /ˈwɪndfɔːl/
windfall
思いがけない利益
Meaning
an unexpected piece of good fortune, typically a large amount of money
Example
The startup received a windfall when a major client paid for a full year in advance.
スタートアップは重要な顧客が1年分前払いした際に思いがけない利益を得ました。