The Collaborative International Dictionary of English v.0.48:

biotin \bi"o*tin\ n.
   a B vitamin (C10H16N2O3S) that aids in body growth; --
   called also vitamin H and coenzyme R. It functions as a
   coenzyme in many carboxylation reactions.

   Note: Biotin binds tightly to the substance avidin, found in
         raw egg-whites. Rats or chick on a diet high in raw
         egg-white may develop skin lesions and retarded growth,
         which can be prevented by adding biotin to the diet.
         --[MI11]

   Syn: .
        [WordNet 1.5 +PJC]