treacherous Definition

treacherous
adj

1. Said of someone, their conduct, etc: not to be trusted; ready or likely to betray.

Thesaurus: traitorous, false-hearted, deceitful, unfaithful, two-faced, Janus-faced, duplicitous, deceiving, false.
2. Hazardous or dangerous; unreliable or untrustworthy.

Example: Black ice made the roads treacherous
Thesaurus: dangerous, risky, tricky, precarious, difficult, unreliable, deceptive, untrustworthy, unstable; Antonym: reliable, dependable, steady.

Derivative: treacherously
adverb

Derivative: treacherousness
noun

Etymology: 14c: from French trechier to cheat.