A guardian or defender against theft or illegal practices or waste.

Roget 753: keeper, custodian, custos [Lat.], ranger, warder, jailer, gaoler, turnkey, castellan^†, guard; watchdog, watchman; Charley; chokidar^†, durwan^†, hayward^†; sentry, sentinel; watch and ward; concierge, coast guard, guarda costa [Sp.], game keeper.    escort, bodyguard.    protector, governor, duenna [Sp.]; guardian; governess etc. (teacher) 540; nurse, nanny, babysitter, catsitter, dogsitter, bonne [Fr.], ayah^†.    ... show more

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.    ... show more

Roget 664: safety, security, surety, impregnability; invulnerability, invulnerableness etc. adj.; danger past, danger over; storm blown over; coast clear; escape etc. 671; means of escape; blow valve, safety valve, release valve, sniffing valve; safeguard, palladium.    guardianship, wardship, wardenship; tutelage, custody, safekeeping; preservation etc. 670; protection, auspices.    safe-conduct, escort, convoy; guard, shield etc. (defense) 717; guardian angel; tutelary god, tutelary deity, tutelary saint; genius loci.    protector, guardian; warden, warder; preserver, custodian, duenna [Sp.], chaperon, third person.    watchdog, bandog^†; Cerberus; watchman, patrolman, policeman; cop [Slang], dick [Slang], fuzz [Slang], smokey [Slang], peeler [Slang], zarp [Slang]; sentinel, sentry, scout etc. (warning) 668; garrison; guardship^†.    [Means of safety] refuge &c., anchor etc. 666; precaution etc. (preparation) 673; quarantine, cordon sanitaire [Fr.].    [Sense of security]. confidence etc. 858 ... show more

A dog trained to guard property.

synonym: guard dog.

Dutch: waakhond
Polish: pies łańcuchowy, pies podwórzowy