any of several species of small burrowing insect-eating mammals with tiny eyes, concealed ears, and soft fur: Talpa europaea and other species
a spy operating from a well-established position of trust esp within the security organization of a government
a person who spends a long period of time establishing a position of trust within an institution in order secretly to further the interests of a rival organization or government, e.g. by spying
a person who leaks secret information about an organization in which they are involved
[Middle English; related to Middle Low German mol]