What does mole mean?
The word “mole” is most commonly used for a small, burrowing mammal that lives beneath the surface of the ground. Moles have pointed snouts, sensitive senses that help them navigate and locate food underground, and specialized front teeth for digging. The word has several specialized meanings as well. In medicine, it refers to a usually benign pigmented growth on the skin. In intelligence and security contexts, a mole is someone who secretly works for one organization while appearing to serve another. In chemistry, a mole is the SI unit for measuring the amount of a substance. A mole is also a massive defensive structure built around a harbour entrance. Because the spelling remains unchanged across these senses, the surrounding context is essential for identifying the intended meaning.
A small, burrowing mammal with velvety fur, a pointed snout, and prominent digging teeth.
"The mole tunneled beneath the lawn and left a ridge of soil behind."
Also used attributively, as in “mole tunnel” and “molehill.”
A dark or flesh-colored raised growth on the skin, usually benign.
"The dermatologist examined the mole for changes in shape or color."
In medical contexts, the term is usually distinguished from other kinds of skin lesions and does not by itself indicate malignancy.
A person who secretly joins an organization or group in order to pass information to another party.
"The agency uncovered a mole who had been copying classified reports."
Common in espionage, intelligence, and investigative contexts; it usually implies concealed allegiance and deliberate intelligence-gathering.
The SI unit for measuring the amount of a substance, equal to the amount containing exactly 6.02214076 × 10^23 elementary entities.
"The reaction required two moles of hydrogen and one mole of oxygen."
The unit is named “mole” and is abbreviated mol; one mole does not mean a mass, but an amount of a substance.
The standard plural is “moles,” as in “a group of moles” or “several skin moles.”
"Several moles had appeared in the lawn overnight."
A mole is nature’s underground engineer: its tunnels can stretch for miles, and its sensitive snout can detect prey and obstacles in complete darkness.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does mole come from?
The animal meaning of “mole” comes through Middle English from Old English, where the word referred to a burrowing animal. The modern word’s exact Germanic ancestry is sometimes described differently in historical sources, so its deeper origin is less certain. The medical sense developed from the resemblance between a pigmented skin growth and the small dark animal. The espionage sense, recorded in the 20th century, is a figurative use suggesting an infiltrator hidden within a group. The chemical unit takes its name from the Italian physicist Amedeo Avogadro and ultimately Latin “moles,” meaning a large mass or quantity.
Related word forms
How mole is actually used
The meaning varies by context. In medicine, a mole is a melanocytic skin growth; in chemistry, a mole is an amount of substance measured in SI units; and in espionage, a mole is a covert informant. The animal sense is the most common in everyday general usage.