GNU Collaborative International Dictionary of English

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1.       
   Sienna , n. [It. terra di Siena, fr. Siena in Italy.] (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.
   1913 Webster
   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.
   1913 Webster