The Collaborative International Dictionary of English v.0.48:

Staunch \Staunch\ (st[aum]nch), Staunchly \Staunch"ly\,
Staunchness \Staunch"ness\, etc.
   See Stanch, Stanchly, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

staunchly
    adv 1: in a staunch manner; "he staunchly defended his
           principles" [syn: staunchly, stanchly]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "staunchly":
   bec et ongles, bona fide, committedly, consistently, constantly,
   deafeningly, decidedly, decisively, determinedly, devotedly,
   earnestly, faithfully, firmly, fixedly, forcefully, forcibly,
   hammer and tongs, heart and soul, heartily, imperviously,
   impregnably, in all seriousness, in earnest, in good earnest,
   in good faith, inflexibly, intensely, invincibly, invulnerably,
   irresistibly, like a bulldog, like a leech, loudly, loyally,
   lustily, mightily, obstinately, perseveringly, persistently,
   powerfully, pungently, purposefully, relentlessly, resistantly,
   resolutely, resolvedly, responsibly, robustly, ruggedly, seriously,
   sincerely, singlemindedly, soundly, stalwartly, steadfastly,
   steadily, stoutly, strongly, sturdily, tenaciously, tooth and nail,
   unswervingly, unyieldingly, vigorously, wholeheartedly,
   with a will, with constancy, with good faith,
   with total dedication