adj.

1. Marked by betrayal of fidelity, confidence, or trust; perfidious. See synonyms at faithless.
2. Not to be relied on; not dependable or trustworthy.
3. Marked by unforeseen hazards; dangerous or deceptive: treacherous waters.

treacherously treach'er·ous·ly adv.
treacherousness treach'er·ous·ness n.

adjective

1. Not true to duty or obligation: disloyal, faithless, false, false-hearted, perfidious, recreant, traitorous, unfaithful, untrue. See continue/stop/pause, trust/distrust.
2. Involving possible risk, loss, or injury: adventurous, chancy, dangerous, hazardous, jeopardous, parlous, perilous, risky, unsafe, venturesome, venturous. Slang hairy. See safety/danger.

adj

Definition: dangerous
Antonyms: harmless, untreacherous

adj

Definition: dishonest, disloyal
Antonyms: forthright, honest, loyal, true

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IN BRIEF: Dangerously unstable and unpredictable.

Life is short, the art long, opportunity fleeting, experience treacherous, judgment difficult. — Hippocrates (c.460-400 BC)

Dansk (Danish)
adj. - lumsk, upålidelig, troløs

Nederlands (Dutch)
onbetrouwbaar, verraderlijk

Français (French)
adj. - traître, très dangereux

Deutsch (German)
adj. - verräterisch

Ελληνική (Greek)
adj. - προδοτικός, δόλιος, ύπουλος, απατηλός, επικίνδυνος, άστατος

Italiano (Italian)
infido, traditore

Português (Portuguese)
adj. - traidor, traiçoeiro, desleal, falso

Русский (Russian)
вероломный, предательский, ненадежный

Español (Spanish)
adj. - traicionero, traidor

Svenska (Swedish)
adj. - förrädisk, bedräglig

中文（简体） (Chinese (Simplified))
背叛的, 奸诈的, 背信弃义的

中文（繁體） (Chinese (Traditional))
adj. - 背叛的, 奸詐的, 背信棄義的

한국어 (Korean)
adj. - 배반하는, 믿을 수 없는

日本語 (Japanese)
adj. - 裏切る, 油断のならない, たよりにならない, あてにならない, 危険な, 不実な

العربيه (Arabic)
‏(صفه) غرار, غادر, خائن‏

עברית (Hebrew)
adj. - ‮בוגדני, מסוכן, שאין לבטוח בו‬

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