Sienna \Si*en"na\, 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.

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.

Source: Webster's Revised Unabridged Dictionary (1913)