treacherous

adj

Etymology: From Old French trecheros, tricheros (“deceitful”), equivalent to treacher + -ous. See treacher.

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.”