Definitions of B:

• noun:   the 2nd letter of the Roman alphabet
• noun:   the blood group whose red cells carry the B antigen
• noun:   (physics) a unit of nuclear cross section; the effective circular area that one particle presents to another as a target for an encounter
• noun:   a logarithmic unit of sound intensity equal to 10 decibels
• noun:   a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder
• noun:   aerobic rod-shaped spore-producing bacterium; often occurring in chainlike formations; found primarily in soil
• noun:   originally thought to be a single vitamin but now separated into several B vitamins