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”).

Probably an alteration of balmy (“foolish; slightly crazy or mad, eccentric”), influenced by barm (“foam rising upon beer or other malt liquors when fermenting, and used as leaven”) (see etymology 1).

Borrowed from Russian бармы (barmy).