say it: TRECH-ur-uhs
treacherous is an adjective meaning "dangerously unstable and unpredictable". It carries 2 recorded senses.
dangerously unstable and unpredictable
“treacherous winding roads”
“an unreliable trestle”
tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans
“Punic faith”
“the perfidious Judas”
“the fiercest and most treacherous of foes”
“treacherous intrigues”
Definitions, synonyms and semantic relations for treacherous come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.