any of various small insectivorous mammals, especially of the family Talpidae, living chiefly underground, and having velvety fur, very small eyes, and strong forefeet: I stopped hating the moles in my rose garden when I realized they were eating the Japanese beetle grubs.

a spy who becomes part of and works from within the ranks of an enemy governmental staff or intelligence agency: There is always a risk that the mole may defect to the enemy. Compare double agent