Windfall/ˈwɪndfɔːl/ Definition 1 of 3Pro Tip 1/3Positive Context Windfall usually implies a positive event or good fortune. Her investment returned a windfall. Pro Tip 2/3Unexpected Surprise A windfall comes without warning, surprising the recipient. A tax rebate brought me an unexpected windfall. Pro Tip 3/3Not Merited The gain is often unrelated to personal effort or work. The economic upturn caused a windfall for investors.