The Collaborative International Dictionary of English v.0.48:

Simply \Sim"ply\, adv.
   1. In a simple manner or state; considered in or by itself;
      without addition; along; merely; solely; barely.
      [1913 Webster]

            [They] make that now good or evil, . . . which
            otherwise of itself were not simply the one or the
            other.                                --Hooker.
      [1913 Webster]

            Simply the thing I am
            Shall make me live.                   --Shak.
      [1913 Webster]

   2. Plainly; without art or subtlety.
      [1913 Webster]

            Subverting worldly strong and worldly wise
            By simply meek.                       --Milton.
      [1913 Webster]

   3. Weakly; foolishly. --Johnson.
      [1913 Webster] Simulacher

WordNet (r) 3.0 (2006):

simply
    adv 1: and nothing more; "I was merely asking"; "it is simply a
           matter of time"; "just a scratch"; "he was only a child";
           "hopes that last but a moment" [syn: merely, simply,
           just, only, but]
    2: absolutely; "I just can't take it anymore"; "he was just
       grand as Romeo"; "it's simply beautiful!" [syn: just,
       simply]
    3: absolutely; altogether; really; "we are simply broke"
    4: in a simple manner; without extravagance or embellishment;
       "she was dressed plainly"; "they lived very simply" [syn:
       plainly, simply]

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "simply":
   absolutely, aesthetically, after a fashion, alone, altogether,
   appreciably, apprehensibly, articulately, artistically, artlessly,
   ascetically, at any rate, at best, at least, at most, at the least,
   at the most, at the outside, at worst, austerely, barely,
   becomingly, but, casually, clearly, coherently, commonly,
   commonplacely, comparatively, completely, comprehensibly, decently,
   decorously, definitely, detectably, distinctly, easily,
   effortlessly, elegantly, en famille, entirely, exclusively,
   explicitly, expressly, facilely, fairly, familiarly, fully,
   genteelly, genuinely, gracefully, guilelessly, hands down,
   in a manner, in a way, in good taste, in part, in plain English,
   in plain terms, in plain words, in some measure, incompletely,
   informally, ingenuously, innocently, integrally, intelligibly,
   irreducibly, just, leastwise, lightly, like clockwork,
   like nothing, limpidly, lucidly, matter-of-factly, merely, mildly,
   moderately, modestly, naturally, no sweat, not comprehensively,
   not exhaustively, obviously, offhand, offhandedly, on easy terms,
   only, openheartedly, openly, ordinarily, part, partially, partly,
   pellucidly, perspicuously, plainly, point-blank, pro tanto,
   properly, prosaically, purely, quietly, readily, really,
   relatively, relaxedly, sans ceremonie, seemly, severely,
   simply and solely, singly, smoothly, so far, solely, somewhat,
   sparely, sparsely, starkly, swimmingly, tastefully, thus far,
   to a degree, to some degree, to the point, tolerably, totally,
   unaffectedly, unambiguously, unanalyzably, unassumingly,
   unceremoniously, unconstrainedly, understandably, undividedly,
   unequivocally, unmistakably, unobtrusively, unofficially,
   unpretentiously, unreservedly, visibly, wholly, with taste,
   without ceremony, without difficulty