| spy(noun, person, plant, mole, sleeper) |
| spook(noun, plant, agent, operative, informer) |
| agent(noun, plant, operative, informer, mole) |
| detective(noun, plant, agent, operative, informer) |
| double agent(noun, expression, plant, agent, operative) |
| emissary(noun, plant, agent, operative, mole) |
| espionage agent(noun, expression, plant, agent, operative) |
| informer(noun, plant, agent, operative, mole) |
| inside agent(noun, expression, plant, agent, operative) |
| intelligencer(noun, plant, agent, spy, operative) |
| investigator(noun, plant, agent, operative, informer) |
| lookout(noun, plant, agent, operative, informer) |
| mole(noun, plant, agent, operative, informer) |
| observer(noun, plant, agent, operative, informer) |
| operative(noun, plant, agent, mole, infiltrator) |
| patrol(noun, plant, agent, operative, informer) |
| picket(noun, plant, agent, operative, informer) |
| plant(noun, agent, operative, informer, mole) |
| scout(noun, plant, agent, operative, informer) |
| secret agent(noun, expression, plant, agent, operative) |