1. [syn: faithlessly, traitorously, treacherously, treasonably, false]
The Collaborative International Dictionary of English v.0.48:
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.
Loyal father of a treacherous son. --Shak.
The treacherous smile, a mask for secret hate.
Syn: Faithless; perfidious; traitorous; false; insidious;
[1913 Webster] -- Treach"er*ous*ly, adv. --
WordNet (r) 3.0 (2006):
adv 1: in a disloyal and faithless manner; "he behaved
treacherously"; "his wife played him false" [syn:
faithlessly, traitorously, treacherously,