ˌdouble ˈagent noun [countable]
someone who finds out an enemy country’s secrets for their own country but who also gives secrets to the enemy ⇒ spy

[TahlilGaran] Dictionary of Contemporary English ▲

spy someone whose job is to find out secret information about another country:
Stalin controlled a network of spies.
The film is basically a spy story.
agent/secret agent someone who works for a government or police department in order to get secret information about another country or organization:
a secret agent working for MI5
He is the FBI’s best undercover agent (=one who works secretly and pretends to be someone else).
double agent someone who finds out an enemy country’s secrets for their own country but who also gives secrets to the enemy:
a former CIA double agent who also worked for the KGB
mole someone who works for an organization while secretly giving information to its enemies:
A mole in the government was leaking information to the press.
informer someone who secretly tells the police about criminal activities, especially for money:
Acting on information from an informer, the police raided the house.
espionage the work that spies do:
He is serving a 20-year prison sentence for espionage.
spying the action of secretly collecting information about a person, country, or organization:
Several embassy officials had been arrested for spying.
surveillance activity in which the police, army, etc watch a person or place carefully because they may be connected with criminal activities:
24-hour surveillance of the building
The police have had him under surveillance (=have been watching him)for months.
covert operations secret military activities against an enemy:
These planes are used by British Intelligence for covert operations.

[TahlilGaran] English Thesaurus ▲