b

B (http://definr.com/B)

     n 1: the blood group whose red cells carry the B antigen [syn: B,
           type B, group B]
     2: aerobic rod-shaped spore-producing bacterium; often
        occurring in chainlike formations [syn: bacillus, bacilli,
         B]
     3: originally thought to be a single vitamin but now separated
        into several B vitamins [syn: B-complex vitamin, {B
        complex}, vitamin B complex, vitamin B, B vitamin, B]
     4: a trivalent metalloid element; occurs both in a hard black
        crystal and in the form of a yellow or brown powder [syn:
        boron, B, atomic number 5]
     5: a logarithmic unit of sound intensity equal to 10 decibels
        [syn: bel, B]
     6: (atomic or nuclear physics) a unit of nuclear cross section;
        the effective circular area that one particle presents to
        another as a target for an encounter [syn: barn]
     7: the 2nd letter of the Roman alphabet [syn: B]