The Collaborative International Dictionary of English v.0.48:

Tacamahac \Tac"a*ma*hac`\, Tacamahaca \Tac`a*ma*ha"ca\, n.
   1. A bitter balsamic resin obtained from tropical American
      trees of the genus Elaphrium (Elaphrium tomentosum and
      Elaphrium Tacamahaca), and also from East Indian trees
      of the genus Calophyllum; also, the resinous exhudation
      of the balsam poplar.
      [1913 Webster]

   2. (Bot.) Any tree yielding tacamahac resin, especially, in
      North America, the balsam poplar, or balm of Gilead
      (Populus balsamifera).
      [1913 Webster]

WordNet (r) 3.0 (2006):

tacamahac
    n 1: poplar of northeastern North America with broad heart-
         shaped leaves [syn: balsam poplar, hackmatack,
         tacamahac, Populus balsamifera]