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…. Definition of treacherous adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. 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. 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 TREACHEROUS definition: characterized by faithlessness or readiness to betray trust; traitorous. See examples of treacherous used in a sentence. of or relating to treachery: the treacherous tyrant who stabbed his friends in the back. unstable or insecure; hazardous: treacherous footing on the icy ….