Especially in Jewish usage: madness, craziness; nonsense, foolishness; (as a count noun) a foolish idea; a foible, an idiosyncracy.
Origin
Late 19th century; earliest use found in Israel Zangwill (1864–1926), writer and advocate of Jewish causes. From Yiddish meshugas from Hebrew mĕšuggaʿaṯ, use as abstract noun of feminine of mĕšuggaʿ.