\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.