Source : Webster's Revised Unabridged Dictionary (1913)

Quaking \Quak"ing\,
   a. & n. from {Quake}, v.

   {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}.

Source : WordNet®

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