Dilator

from WordNet (r) 3.0 (2006)

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: {dilator}, {dilater}]

from The Collaborative International Dictionary of English v.0.48

Dilator \Di*lat"or\, n. [See {Dilate}.]
   1. One who, or that which, widens or expands.
      [1913 Webster]

   2. (Anat.) A muscle that dilates any part.
      [1913 Webster]

   3. (Med.) An instrument for expanding a part; as, a urethral
      dilator.
      [1913 Webster]