I need more context to understand what you’re looking for. Here are some possibilities for “extra (agent) 4 letters”:
- Spy: A secret agent who gathers information or carries out covert operations.
- Scout: Someone who is sent ahead to gather information about an enemy or explore new territory.
- Aide: Someone who helps and assists another person, often a person of high rank or importance.
- Temp: A temporary worker who is hired to fill a job opening for a short period of time.
- Mole: An undercover agent who infiltrates an organization to gather information.
If you can give me more information about the context in which you heard or saw this phrase, I may be able to give you a more specific answer.