BALDERDASH is a 10 letter word that starts with B.

1. \Bal"der*dash\, n. [Of uncertain origin: cf. Dan.
   balder noise, clatter, and E. dash; hence, perhaps, unmeaning
   noise, then hodgepodge, mixture; or W. baldorduss a
   prattling, baldordd, baldorddi, to prattle.]
   1. A worthless mixture, especially of liquors.
            Indeed beer, by a mixture of wine, hath lost both
            name and nature, and is called balderdash. --Taylor
                                                  (Drink and
                                                  Welcome).
   2. Senseless jargon; ribaldry; nonsense; trash.
   

2. \Bal"der*dash\, v. t.
   To mix or adulterate, as liquors.
         The wine merchants of Nice brew and balderdash, and
         even mix it with pigeon's dung and quicklime.
                                                  --Smollett.