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]

The Collaborative International Dictionary of English v.0.48:

Quaking \Quak"ing\,
   a. & n. from Quake, v.
   [1913 Webster]

   Quaking aspen (Bot.), an American species of poplar
      (Populus tremuloides), the leaves of which tremble in
      the lightest breeze. It much resembles the European aspen.
      See Aspen.

   Quaking bog, a bog of forming peat so saturated with water
      that it shakes when trodden upon.

   Quaking grass. (Bot.)
   (a) One of several grasses of the genus Briza, having
       slender-stalked and pendulous ovate spikelets, which
       quake and rattle in the wind. Briza maxima is the large
       quaking grass; Briza media and Briza minor are the
       smaller kinds.
   (b) Rattlesnake grass (Glyceria Canadensis).
       [1913 Webster]

WordNet (r) 3.0 (2006):

Populus tremuloides
    n 1: slender aspen native to North America [syn: American
         quaking aspen, American aspen, Populus tremuloides]