dilator

1. A muscle that dilates a body part, such as a blood vessel or the pupil of the eye.
2. An instrument that dilates a body part, such as a cavity, canal, or orifice.

1. An instrument or a substance for enlarging a cavity, canal, blood vessel, or opening.
2. A muscle that dilates an orifice or a body part, such as a blood vessel or the pupil of the eye. Also called dilatator.

A structure (muscle) that dilates, or an instrument used to dilate.

• d. pupillae muscle — dilator muscle of the pupil.

The noun has 3 meanings:

Meaning #1: a muscle or nerve that dilates or widens a body part

Meaning #2: a drug that causes dilation

Meaning #3: a surgical instrument that is used to dilate or distend an opening or an organ
  Synonym: dilater