barmy

From barm (“foam rising upon beer or other malt liquors when fermenting, and used as leaven”) + -y (suffix meaning ‘having the quality of’ forming adjectives). Barm is derived from Middle English berm, berme (“foam rising upon ale or beer fermenting; leaven, yeast; foam or head of beer produced by pouring”) [and other forms], from Old English beorma (“foam or head of beer; leaven, yeast”), from Proto-West Germanic *bermō (“barm; yeast”); further etymology uncertain, perhaps from Proto-Indo-European *bʰrewh₁- (“to boil; to brew”) or *gʷʰer- (“warm; hot”).

出典: Wiktionary「barmy」（CC BY-SA 4.0）