spy satellite(n = noun.artifact) - a satellite with sensors to detect nuclear explosions;
is a kind of artificial satellite, orbiter, satellite

N  warning, early warning, caution, caveat, notice, premonition, premonishment, prediction, contraindication, lesson, dehortation, admonition, monition, alarm, 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, 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, monitor, guard camera, radar, AWACS, spy satellite, spy-in-the- sky, U2 plane, spy plane, warning, premonitory, monitory, cautionary, admonitory, admonitive, sematic, warned, forewarned, on one's guard, in terrorem, Int, beware!, ware!, take care!, look out!, fore (golf), mind what you are about!, take care what you are about!, mind!, ne reveillez pas le chat qui dort, don't wake a sleeping cat, foenum habet in cornu, caveat actor, le silence du people est la legon des rois, verbum sat sapienti, a word to the wise is sufficient, un averti en vaut deux.

artificial satellite, astronomy satellite, communications satellite, galilean satellite, meteorological satellite, northern spy, satellite, satellite receiver, satellite television, satellite transmitter, satellite tv, spy, weather satellite