military A secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors.
synonym: spy.
Roget 668:
warning,
early warning,
caution,
caveat;
notice
etc.
(information)
527;
premonition,
premonishment†;
prediction
etc.
511;
contraindication,
lesson,
dehortation†;
admonition,
monition;
alarm
etc.
669.
handwriting on the wall,
mene mene tekel upharsin,
red flag,
yellow flag;
fog-signal,
foghorn;
siren;
monitor,
warning voice,
Cassandra†,
signs of the times,
Mother Cary's chickens†,
stormy petrel,
bird of ill omen,
gathering clouds,
clouds in the horizon,
death watch.
watchtower,
beacon,
signal post;
lighthouse
etc.
(indication of locality)
550.
sentinel,
sentry, ,
watch,
watchman;
watch and ward;
watchdog,
bandog†,
housedog†;
patrol,
patrolman,
vedette†,
picket,
bivouac,
scout,
spy,
spial†;
undercover agent,
mole,
plainclothesman;
advanced guard,
rear guard;
lookout.
cautiousness
etc.
864.
monitor,
guard camera,
radar,
AWACS,
spy satellite,
spy-in-the-sky,
U2 plane,
spy plane.
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Dutch: geheim agent, dwarskijker, spion, verspieder
Polish: wywiadowca, szpieg, agent, agent wywiadu