treacherous

adjective3

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 […] — 1855
2. •
   Unreliable; dangerous.

   • 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. — 1959
3. •
   Deceitful; inclined to betray.