| mouthpiece |
| 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 service(noun, expression, plant, agent, operative) |
| sleeper(noun, plant, agent, spy, operative) |
| sleuth(noun, plant, agent, operative, informer) |
| snoop(noun, plant, agent, operative, informer) |
| spier |
| spook(noun, plant, agent, operative, informer) |
| spotter(noun, plant, agent, spy, operative) |
| teller |
| undercover agent(noun, expression, plant, agent, operative) |
| watcher(noun, plant, agent, operative, informer) |
| advocate |
| alarmist |
| ancestor |