| spy(noun, person, plant, watch, operative) |
| agent(noun, plant, spy, operative, informer) |
| secret agent(noun, expression, plant, agent, spy) |
| double agent(noun, expression, plant, agent, spy) |
| counterspy |
| detective(noun, plant, watch, agent, spy) |
| emissary(noun, plant, watch, agent, spy) |
| espionage agent(noun, expression, plant, agent, operative) |
| foreign agent(noun, expression, plant, agent, operative) |
| informer(noun, plant, agent, spy, operative) |
| inside agent(noun, expression, plant, agent, operative) |
| intelligence agent |
| intelligencer(noun, plant, agent, spy, operative) |
| investigator(noun, plant, agent, operative, informer) |
| lookout(noun, plant, watch, agent, spy) |
| mole(noun, plant, watch, agent, spy) |
| observer(noun, plant, agent, operative, informer) |
| operative(noun, plant, agent, spy, mole) |
| patrol(noun, plant, watch, agent, spy) |
| picket(noun, plant, watch, agent, spy) |