[1] : The Collaborative International Dictionary of English v.0.48

faithless \faith"less\, a.
   1. not believing; not giving credit.
      1913 webster

            be not faithless, but believing.      --john xx. 27.
      1913 webster

   2. not believing on god or religion; specifically, not
      believing in the christian religion. --shak.
      1913 webster

   3. not observant of promises or covenants.
      1913 webster

   4. not true to allegiance, duty, or vows; perfidious;
      trecherous; disloyal; not of true fidelity; inconstant, as
      a husband or a wife.
      1913 webster

            a most unnatural and faithless service. --shak.
      1913 webster

   5. serving to disappoint or deceive; delusive; unsatisfying.
      "yonder faithless phantom." --goldsmith. --
      faith"lessly, adv.faith"lessness, n.
      1913 webster
see also:
faith"lessly faith"lessness 

[2] : WordNet (r) 2.0

faithlessly
     adv : in a disloyal and faithless manner; "he behaved
           treacherously"; "his wife played him false" syn: traitorously,
            treacherously, treasonably, false
see also:
traitorously treacherously treasonably false 

Faithlessly >> F Words
Faithlessly, definition of term: Faithlessly
faithlessly_pag1.html