treacherous

adj

1. Exhibiting treachery.

   “I see the wife misused by her husband, I see the treacherous seducer of young women, / I mark the ranklings of jealousy and unrequited love attempted to be hid […]”

2. Deceitful; inclined to betray.
3. Unreliable; dangerous.

   “a treacherous mountain trail”

   “Work on the muskeg resulted in the formation in the first instance, and later in lengths of newly-laid track disappearing without trace into the treacherous bog.”

   “[…] they stood in the region of perpetual snow, amidst the glittering, treacherous glaciers and crevasses, with vast slippery-pathed precipices yawning round.”

   “There are many treacherous paths leading toward history’s realms of darkness, but when it comes to routes hacked out by imperialist powers in the Congo, we really do seem near darkness’s heart.”

   “It is standard practice for search and rescue authorities to ask other vessels in the area to assist. Usually, this is done. The weather on the night of 31 December was too atrocious, and when at 11pm the Coast Guard asked the crabber Ruff & Reddy to head to the scene, its skipper refused, as a skipper has a right to do if he believes conditions to be too treacherous.”