Si·en·na n.  Chem. Clay that is colored red or brown by the oxides of iron or manganese, and used as a pigment. It is used either in the raw state or burnt.
  Burnt sienna, sienna made of a much redder color by the action of fire.
  Raw sienna, sienna in its natural state, of a transparent yellowish brown color.
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  burnt sienna
       n 1: a shade of brown with a tinge of red [syn: reddish brown,
            sepia, Venetian red]
       2: a reddish-brown pigment produced by roasting sienna