The Collaborative International Dictionary of English v.0.48:

Faithful \Faith"ful\, a.
   1. Full of faith, or having faith; disposed to believe,
      especially in the declarations and promises of God.
      [1913 Webster]

            You are not faithful, sir.            --B. Jonson.
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   2. Firm in adherence to promises, oaths, contracts, treaties,
      or other engagements.
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            The faithful God, which keepeth covenant and mercy
            with them that love him.              --Deut. vii.
                                                  9.
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   3. True and constant in affection or allegiance to a person
      to whom one is bound by a vow, by ties of love, gratitude,
      or honor, as to a husband, a prince, a friend; firm in the
      observance of duty; loyal; of true fidelity; as, a
      faithful husband or servant.
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            So spake the seraph Abdiel, faithful found,
            Among the faithless, faithful only he. --Milton.
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   4. Worthy of confidence and belief; conformable to truth ot
      fact; exact; accurate; as, a faithful narrative or
      representation.
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            It is a faithful saying.              --2 Tim. ii.
                                                  11.
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   The Faithful, the adherents of any system of religious
      belief; esp. used as an epithet of the followers of
      Mohammed.

   Syn: Trusty; honest; upright; sincere; veracious;
        trustworthy. -- Faith"ful*ly, adv. -Faith"ful*ness,
        n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

faithfully
    adv 1: in a faithful manner; "it always came on, faithfully,
           like the radio" [syn: faithfully, dependably,
           reliably] [ant: undependably, unfaithfully,
           unreliably]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "faithfully":
   absolutely, acquiescently, assiduously, bona fide, compliantly,
   consistently, constantly, dead, definitely, descriptively,
   devotedly, diligently, directly, doggedly, duteously, dutifully,
   even, exactly, expressively, expressly, firmly, graphically,
   in all respects, in compliance with, in conformity with,
   in every respect, in good faith, in obedience to, indefatigably,
   industriously, insistently, ipsissimis verbis, just, literally,
   literatim, loyally, naturalistically, obediently, patiently,
   perseveringly, persistently, persistingly, pertinaciously,
   ploddingly, plumb, point-blank, positively, precisely,
   realistically, relentlessly, representatively, resolutely,
   responsibly, right, rigidly, rigorously, sedulously, sloggingly,
   square, squarely, staunchly, steadfastly, steadily, straight,
   strictly, submissively, tenaciously, tirelessly, to the letter,
   unabatingly, undeviatingly, unerringly, unfalteringly,
   unflaggingly, unflinchingly, unintermittingly, uninterruptedly,
   unrelentingly, unremittingly, unrestingly, unsleepingly,
   unswervingly, untiringly, unwaveringly, unwearyingly, verbally,
   verbatim, verbatim et litteratim, vividly, wearilessly, willingly,
   with good faith, word by word, word for word