The Collaborative International Dictionary of English v.0.48:

Tamarack \Tam"a*rack\, n. (Bot.)
   (a) The American larch; also, the larch of Oregon and British
       Columbia (Larix occidentalis). See Hackmatack, and
       Larch.
   (b) The black pine (Pinus Murrayana) of Alaska, California,
       etc. It is a small tree with fine-grained wood.
       [1913 Webster]

WordNet (r) 3.0 (2006):

Larix occidentalis
    n 1: tall larch of western North America have pale green sharply
         pointed leaves and oblong cones; an important timber tree
         [syn: western larch, western tamarack, Oregon larch,
         Larix occidentalis]