mole

noun

1. 1.

   A small burrowing mammal with dark velvety fur, a long muzzle, and very small eyes.

2. 2.

   A small, often slightly raised, dark blemish on the skin.

3. 3.

   (chemistry) The SI unit of amount of substance, equal to approximately 6.022 x 10^23 particles.

4. 4.

   A spy who becomes part of an enemy organization.