Treacherous, a.
Etymology: [See Treacher.]
Like a traitor; involving treachery; violating allegiance or faith pledged; traitorous to the state or sovereign; perfidious in private life; betraying a trust; faithless. Loyal father of a treacherous son. Shak. The treacherous smile, a mask for secret hate. Cowper.
Syn. -- Faithless; perfidious; traitorous; false; insidious; plotting. -- Treach"er*ous*ly, adv. -- Treach"er*ous*ness, n.
Shades of meaning
Fernald lists treacherous only as an antonym, under honest.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given