mole
n. countablen. a small, dark spot on your skin that you are usually born with. It can also be a small animal with dark fur that lives in tunnels underground.
n. a small, permanent dark spot on the human skin; alternatively, a small burrowing insectivorous mammal with dark velvety fur and very small eyes.
The doctor checked the mole on my arm to make sure it was healthy.
A mole had ruined the garden by digging long tunnels under the lawn and pushing up piles of dirt.
While most moles are benign skin growths, any change in their symmetry or colour should be evaluated by a dermatologist to rule out malignancy.
From Latin mola (“mill”), or otherwise a back-formation from Molesey (“Mul's Island”).
In a political or corporate context, refers to a spy who works inside an organisation to gather secret information.