treacherously

treacherously
    adv 1: in a disloyal and faithless manner; "he behaved
           treacherously"; "his wife played him false" [syn:
           {faithlessly}, {traitorously}, {treacherously},
           {treasonably}, {false}]
    

Treacherous \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.
   [1913 Webster]

         Loyal father of a treacherous son.       --Shak.
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         The treacherous smile, a mask for secret hate.
                                                  --Cowper.
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   Syn: Faithless; perfidious; traitorous; false; insidious;
        plotting.
        [1913 Webster] -- {Treach"er*ous*ly}, adv. --
        {Treach"er*ous*ness}, n.
        [1913 Webster]