Definition of treacherous adjective from the Oxford Advanced Learner's Dictionary

     

    treacherous

     adjective
    adjective
    BrE BrE//ˈtretʃərəs//
     
    ; NAmE NAmE//ˈtretʃərəs//
     
     
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  1. 1that cannot be trusted; intending to harm you synonym deceitful He was weak, cowardly and treacherous. lying, treacherous words
  2. 2dangerous, especially when seeming safe The ice on the roads made driving conditions treacherous. the mountain’s notoriously treacherous rocky crest
  3. Word Origin Middle English (in sense 1): from Old French trecherous, from trecheor ‘a cheat’, from trechier ‘to cheat’.
See the Oxford Advanced American Dictionary entry: treacherous