Dangerously unstable and unpredictable:
— Treacherous winding roads.

synonym: unreliable.

Tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans:
— The fiercest and most treacherous of foes.
— Treacherous intrigues.

synonyms: perfidious, punic.

Roget 940: dishonest, dishonorable; unconscientious, unscrupulous; fraudulent etc. 545; knavish; disgraceful etc. (disreputable) 974; wicked etc. 945.    false-hearted, disingenuous; unfair, one-sided; double, double-hearted, double-tongued, double-faced; timeserving^†, crooked, tortuous, insidious, Machiavelian, dark, slippery; fishy; perfidious, treacherous, perjured.    infamous, arrant, foul, base, vile, ignominious, blackguard.    contemptible, unrespectable, abject, mean, shabby, little, paltry, dirty, scurvy, scabby, sneaking, groveling, scrubby, rascally, pettifogging; beneath one.    low-minded, low-thoughted^†; base-minded.    undignified, indign^†; unbecoming, unbeseeming^†, unbefitting; derogatory, degrading; infra dignitatem [Lat.], beneath one's dignity; ungentlemanly, ungentlemanlike; unknightly^†, unchivalric^†, unmanly, unhandsome; recreant, inglorious.    corrupt, venal; debased, mongrel.    faithless, of bad faith, false, unfaithful, disloyal; untrustworthy; trustless, trothless^†; lost to shame, dead to honor; barratrous.    ... show more