Synonyms for Treacherous:

adj.

all (adjective)
unreliable.
cowardly (adjective)
recreant.
dangerous (adjective)
faulty, dangerous, hazardous, unsafe, ticklish, perilous, parlous, precarious, shaky, chancy, alarming, risky, difficult, wicked, unstable, threatening, hairy, insecure, ominous, menacing, Jeopardous.
dishonest (adjective)
devious, double-faced, crooked, corrupt, felonious, crafty, unscrupulous, deceptive, underhanded, hypocritical, turncoat, immoral, insincere, dishonest, untrustworthy, deceitful, cheating, untrue, Prevaricating, fraudulent, dishonorable, traitorous, Deceiving.
dishonest, disloyal (adjective)
deceptive, perfidious, faithless, unreliable, untrue, false, tricky, untrustworthy, misleading, unfaithful, deceitful, traitorous, slippery, False-hearted, treasonable, recreant.
disobedient (adjective)
nonconformist, Disobeying, rebellious, contrary, defiant, undisciplined, subversive, unruly, treasonous, insubordinate, traitorous, disloyal, seditious, disobedient, intractable, factious, ungovernable, out of control, Misbehaving, unmanageable, Disregardful, wayward, recalcitrant, mutinous, anarchistic, mischievous.
malevolent (adjective)
baleful, wicked, catty, evil, vicious, spiteful, churlish, baneful, venomous, perfidious, virulent, Black-hearted, mean, hostile, rancorous, corrosive, sullen, vindictive, bitter, malevolent, ill-natured, antagonistic, malicious, sinister, hurtful, nasty, hateful, malignant, foul.
wicked (adjective)
wicked.

n.

disastrous, injurious, harmful, ruinous, damaging. false. faithless, untrue, continue, recreant, trust, False-hearted. chancy, safety, parlous, hairy, venturous, adventurous, venturesome. disloyal (noun)
disaffected.
traitorous (noun)
false, treasonable, faithless.
treacherous (noun)
perfidious, unreliable, dangerous, punic, unfaithful, unsafe.

Other synonyms:

Punic
punic.
false, False-hearted, faithless. parlous, venturous, chancy. hairy, venturesome, adventurous. untrue. disloyal
disaffected.
injurious
harmful.

Usage examples for treacherous

  1. Father and mother were dead- the father drowned in a wild night while trying to make the treacherous mouth of the inadequate harbour, the mother dead of her grief. – An Isle in the Water by Katharine Tynan
  2. I knew that kind of a drift; it is treacherous – Over Prairie Trails by Frederick Philip Grove
  3. I was neither cruel nor treacherous to him," cried Leo. – The Man with a Shadow by George Manville Fenn