The Collaborative International Dictionary of English v.0.48:

Poplar \Pop"lar\, n. [OE. popler, OF. poplier, F. peuplier, fr.
   L. populus poplar.] (Bot.)
   1. Any tree of the genus Populus; also, the timber, which
      is soft, and capable of many uses.
      [1913 Webster]

   Note: The aspen poplar is Populus tremula and Populus
         tremuloides; Balsam poplar is Populus balsamifera;
         Lombardy poplar (Populus dilatata) is a tall, spiry
         tree; white poplar is Populus alba.
         [1913 Webster]

   2. The timber of the tulip tree; -- called also white
      poplar. [U.S.]
      [1913 Webster]