Definition from Wiktionary, the free dictionary
Etymology 1 
From Old English beorma (“yeast”)
Etymology 2 
Probably an alteration of balmy
- (chiefly UK) dotty, goofy, wacko.
- 2004: The movie is sweet enough in its barmy way... -- Roger Ebert
Derived terms 
Usage notes 
- in US English, balmy is usual for sense (2); elsewhere this is occasionally found but some authorities consider it erroneous, despite its probable etymology.