mole

noun

1. 1.A pigmented spot on the skin, a naevus, slightly raised, and sometimes hairy.
2. 2.Any of several small, burrowing insectivores of the family Talpidae.
3. 3.Any of the burrowing rodents also called mole rats.
4. 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.
5. 5.A kind of self-propelled excavator used to form underground drains, or to clear underground pipelines