Source : Webster's Revised Unabridged Dictionary (1913)

Marigold \Mar"i*gold\, n. [Mary + gold.] (Bot.)
   A name for several plants with golden yellow blossoms,
   especially the {Calendula officinalis} (see {Calendula}), and
   the cultivated species of {Tagetes}.

   Note: There are several yellow-flowered plants of different
         genera bearing this name; as, the {African or French
         marigold} of the genus {Tagetes}, of which several
         species and many varieties are found in gardens. They
         are mostly strong-smelling herbs from South America and
         Mexico: {bur marigold}, of the genus {Bidens}; {corn
         marigold}, of the genus {Chrysanthemum} ({C. segetum},
         a pest in the cornfields of Italy); {fig marigold}, of
         the genus {Mesembryanthemum}; {marsh marigold}, of the
         genus {Caltha} ({C. palustris}), commonly known in
         America as the cowslip. See {Marsh Marigold}.

   {Marigold window}. (Arch.) See {Rose window}, under {Rose}.

Source : WordNet®

marigold
     n : any of various tropical American plants of the genus Tagetes
         widely cultivated for their showy yellow or orange
         flowers