The Collaborative International Dictionary of English v.0.48:

Hackmatack \Hack"ma*tack`\ (h[a^]k"m[.a]*t[a^]k`), 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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Larch \Larch\ (l[aum]rch), n. [Cf. OE. larege (Cotgrave), It.
   larice, Sp. larice, alerce, G. l[aum]rche; all fr. L. larix,
   -icis, Gr. la`rix.] (Bot.)
   A genus of coniferous trees, having deciduous leaves, in
   fascicles (see Illust. of Fascicle).

   Note: The European larch is Larix Europ[ae]a. The American
         or black larch is Larix Americana, the hackmatack or
         tamarack. The trees are generally of a drooping,
         graceful appearance.
         [1913 Webster]