BASILAR is a 7 letter word that starts with B.
\Bas"i*lar\, Basilary \Bas"i*la*ry\, a. [F. basilaire, fr. L. basis. See {Base}, n.] 1. Relating to, or situated at, the base. 2. Lower; inferior; applied to impulses or springs of action. [R.] ``Basilar instincts.'' --H. W. Beecher.
WordNet Dictionary