It would be just to slay this treacherous, murderous creature, just and many times deserved; and also it seemed the only safe thing to do.
There the hobbits sat under the cover of the thorny bush, while the drear light of Mordor faded slowly into a deep and starless night; and Sam spoke into Frodo’s ear all that he could find words for of Gollum’s treacherous attack, the horror of Shelob, and his own adventures with the orcs.
There are no more uses of "treacherous" in the book.
Show samples from other sources
The road through Afghanistan’s Kabul gorge is even more treacherous than the Road of Death in Bolivia.
It’s a gorgeous beach, but the waves are treacherous in the water.