The Collaborative International Dictionary of English v.0.48:

Assuredly \As*sur"ed*ly\, adv.
   Certainly; indubitably. "The siege assuredly I'll raise."
   --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

assuredly
    adv 1: without a doubt; "the grammar schools were assuredly not
           intended for the gentry alone"

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "assuredly":
   OK, Roger, absolutely, actually, all right, alright, alrighty,
   amen, and no mistake, as you say, at all events, at any rate, aye,
   by all means, certainly, clearly, da, decidedly, decisively,
   definitely, demonstrably, distinctly, exactly, fine,
   for a certainty, for a fact, for certain, for real, for sure,
   forsooth, good, good enough, hear, in all conscience, in truth,
   indeed, indeedy, indubitably, ja, just so, mais oui, manifestly,
   most assuredly, most certainly, naturally, naturellement,
   nothing else but, noticeably, observably, obviously, of course,
   okay, oui, patently, positively, precisely, quite, rather, really,
   right, righto, sensibly, seriously, sure, sure thing, surely,
   to a certainty, to be sure, truly, unambiguously, undeniably,
   unequivocally, unmistakably, verily, very well, visibly,
   well and good, why yes, without doubt, yea, yeah, yep, yes,
   yes indeed, yes indeedy, yes sir, yes sirree