Asp'en or Asp1, n.
n. [A-S. æspe, æps, æsp, epse, O. H. Ger. aspa, Icel. aspi, Dan. æsp, Sw. asp, D. esp, Ger. espe, üspe, aspe.] (Bot.) One of several species of poplar bearing this name, especially the Populus tremula, so called from the trembling of its leaves, which move with the slightest impulse of the air.