The community oven in France but common in English villages, where the bread was baked not as well as it could be. This bread was called 'banal' as it came from something of common use - from which we have our use of the word 'banal' = ordinary or commonplace. Banal is derived from the *ban, which was the lord's power to punish in everyday matters. [< Fr forn < Lat. furnus = an oven] -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.