O.E.
beorma "yeast," also "head of a beer," from PIE base
*bher- "to boil up" (cf. Du.
berm, M.L.G.
barm, L.
fermentum "substance causing fermentation," Skt.
bhurati "moves convulsively, quivers," M.Ir.
berbaim "I boil, seethe"), from base
*bhreue- "to boil, bubble, effervesce, burn" (see
brew). Hence,
barmy "frothing" (1535); fig. sense of "excitedly active" is attested from 1602. Meaning "foolish" (1892) is probably an alteration of
balmy (see
balm).