n.
an unexpected burst of good news that only makes you skeptical, believing that every sudden rise in your fortunes must inevitably be accompanied by an impending fall, which leaves you feeling uneasy at the end of a really good day, waiting around for the punch line.
Middle English winne, joy + wawe, woe. Compare williwaw, a sudden blast of wind descending from the mountains to the sea. Pronounced “win-uh-waw.”