The Collaborative International Dictionary of English v.0.48:

Sagebrush \Sage"brush`\, n.
   A low irregular shrub (Artemisia tridentata), of the order
   Compositae, covering vast tracts of the dry alkaline
   regions of the American plains; -- called also sagebush,
   and wild sage.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Artemisia \Ar`te*mi"si*a\ ([aum]rt[-e]"m[i^]zh"[i^]*[.a] or
   [aum]rt[-e]"m[i^]sh"[i^]*[.a]), n. [L. Artemisia, Gr.
   'Artemisi`a.] (Bot.)
   A genus of plants including the plants called mugwort,
   southernwood, and wormwood. Of these Artemisia absinthium,
   or common wormwood, is well known, and Artemisia tridentata
   is the sage brush of the Rocky Mountain region.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Artemisia tridentata
    n 1: aromatic shrub of arid regions of western North America
         having hoary leaves [syn: big sagebrush, blue sage,
         Seriphidium tridentatum, Artemisia tridentata]