treacherous
adj.dangerous because of hidden risks or because you cannot trust someone. You use this to describe slippery roads or people who might betray you.
adj.characterised by hidden dangers or hazards; also describes a person who is guilty of deception or betrayal. Often used to describe environmental conditions like ice or currents.
“The mountain roads are treacherous during the winter.”
“The hikers decided to turn back because the narrow path along the cliff became too treacherous in the rain.”
“The protagonist must navigate a treacherous political landscape where today's allies could easily become tomorrow's enemies in the pursuit of power.”
Commonly used both literally for physical hazards and figuratively for social or political betrayal.
“What’s more, to remain in permanent stealth mode in those treacherous depths, megalodon would have needed to undergo some pretty drastic changes.”
From Old French trecheros, tricheros (“deceitful”), equivalent to treacher + -ous. See treacher.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.