Source : Webster's Revised Unabridged Dictionary (1913)

Hackmatack \Hack"ma*tack`\, n. [Of American Indian origin.]
   (Bot.)
   The American larch ({Larix Americana}), a coniferous tree
   with slender deciduous leaves; also, its heavy, close-grained
   timber. Called also {tamarack}.

Source : WordNet®

hackmatack
     n : poplar of northeastern North America with broad heart-shaped
         leaves [syn: {balsam poplar}, {tacamahac}, {Populus
         balsamifera}]