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®

quaking aspen
     n : Old World aspen with a broad much-branched crown;
         northwestern Europe and Siberia to North Africa [syn: {European
         quaking aspen}, {Populus tremula}]