TREACHEROUS definition: characterized by faithlessness or readiness to betray trust; traitorous. See examples of treacherous used in a sentence. May 9, 2026 · faithless, false, disloyal, traitorous, treacherous, perfidious mean untrue to what should command one's fidelity or allegiance. faithless applies to any failure to keep a promise or pledge or … TREACHEROUS definition: 1. If the ground or sea is treacherous, it is extremely dangerous, especially because of bad…. Treacherous means either not trusted or dangerous. A treacherous road might be icy or otherwise likely to cause a car accident. A treacherous friend will betray you. Definition of treacherous adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. Guilty of or characterized by betrayal of confidence or trust; perfidious. Characterized by unforeseen or hidden hazards; dangerous or deceptive: treacherous waters; treacherous footing. Apr 5, 2026 · Adjective treacherous (comparative more treacherous, superlative most treacherous) Exhibiting treachery. Antonym: loyal Definition of treacherous. English dictionary and integrated thesaurus for learners, writers, teachers, and students with advanced, intermediate, and beginner levels.