Treach"er*ous (?), a. [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.
© Webster 1913.