Source : Webster's Revised Unabridged Dictionary (1913)

Depressor \De*press"or\, n.
   1. One who, or that which, presses down; an oppressor.

   2. (Anat.) A muscle that depresses or tends to draw down a
      part.

   {Depressor nerve} (Physiol.), a nerve which lowers the
      activity of an organ; as, the depressor nerve of the
      heart.

Source : WordNet®

depressor
     n 1: any skeletal muscle that draws a part down [syn: {depressor
          muscle}]
     2: any nerve whose activity tends to reduce the activity or
        tone of the body part it serves [syn: {depressor nerve}]
     3: a device used by physician to press a part down or aside