mole

ot noun

1. A pigmented spot on the skin, a naevus, slightly raised, and sometimes hairy.
2. Any of several small, burrowing insectivores of the family Talpidae.
3. Any of the burrowing rodents also called mole rats.
4. An internal spy, a person who involves himself or herself with an enemy organisation, especially an intelligence or governmental organisation, to determine and betray its secrets from within.