Source : Webster's Revised Unabridged Dictionary (1913)

Petal \Pet"al\, n. [Gr. ? a leaf, a leaf or plate of metal, fr.
   ? outspread, broad, flat: cf. F. p['e]tale. See {Fathom}.]
   1. (Bot.) One of the leaves of the corolla, or the colored
      leaves of a flower. See {Corolla}, and Illust. of
      {Flower}.

   2. (Zo["o]l.) One of the expanded ambulacra which form a
      rosette on the black of certain Echini.

Source : WordNet®

petal
     n : part of the perianth that is usually brightly colored [syn:
         {flower petal}]