127 entries under noun topic. ×

1
detective(plant, watch, guard, agent)
1
detector
1
determinist
1
discoverer
1
distinguisher
1
double agent(expression, plant, agent, operative)
1
emissary(plant, agent, operative, mole)
1
espionage agent(expression, plant, agent, operative)
1
foreign agent(expression, plant, agent, operative)
1
gawker(witness, proof, testimony, watcher)
1
hearer
1
imparter
1
informer(plant, agent, operative, mole)
1
inside agent(expression, plant, agent, operative)
1
intelligencer(plant, agent, operative, informer)
1
maintainer
1
marker
1
minder
1
mole(plant, agent, operative, informer)
1
non-participant
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APASmart Define. (2016). observer thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/observer/thesaurus/synonyms
ChicagoSmart Define. 2016. "observer thesaurus" https://smartdefine.org/observer/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2016, observer thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/observer/thesaurus/synonyms>.
MLASmart Define. "observer thesaurus" 26 February 2016. Web. 25 September 2026. <https://smartdefine.org/observer/thesaurus/synonyms>