Mole

Mole - noun [ C ] (ANIMAL) - a small mammal that is almost blind, has dark fur, and lives in passages that it digs underground;
Mole - noun [ C ] (SPOT) a small, dark spot or lump (= raised area) on a person's skin;
Mole - noun [ C ] (PERSON) a person who works for an organization or government and secretly gives information to its competitor or enemy:

[cambridge dictionary.]

Mole: literalmente "Topeira", comemente usado como “agente infiltrado, espião”.

• We knew he was the mole all along. [ Sabíamos que ele era o espião todo o tempo. ]
• There’s a mole in this company and we’re going to find out who it is. [ Tem um espião nessa empresa e vamos descobrir quem é. ]
• A mole inside the Department had leaked secret proposals to the press. [A toupeira dentro do Departamento tinha vazado propostas secretas para a imprensa..]

Fonte: www.englishexpert.com.br