It's no secret that balmy is derived from balm, an aromatic ointment or fragrance that heals or soothes. So when did it come to mean "foolish," you might wonder? Balmy goes back to the 15th century and was often used in contexts referring to weather, such as "a balmy breeze" or, as Mark Twain wrote in Tom Sawyer, "The balmy summer air, the restful quiet...." Around the middle of the 19th century, it developed a new sense suggesting a weak or unbalanced mind. It is uncertain if the soft quality or the soothing effect of balm influenced this use. But later in the century, balmy became altered to barmy in its "crazy" sense. This alteration may have come about from a mix-up with another barmy, meaning "full of froth or ferment." That barmy is from barm, a term for the yeast formed on fermenting malt liquors, which can indeed make one act balmy.