Source : Webster's Revised Unabridged Dictionary (1913)

Dilator \Di*lat"or\, n. [See {Dilate}.]
   1. One who, or that which, widens or expands.

   2. (Anat.) A muscle that dilates any part.

   3. (Med.) An instrument for expanding a part; as, a urethral
      dilator.

Source : WordNet®

dilator
     n 1: a muscle or nerve that dilates or widens a body part
     2: a drug that causes dilation
     3: a surgical instrument that is used to dilate or distend an
        opening or an organ [syn: {dilater}]