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

plainly \plain"ly\, adv.
   in a plain manner; clearly.
   1913 webster

[2] : WordNet (r) 2.0

plainly
     adv 1: unmistakably `plain' is often used informally for
            `plainly'; "the answer is obviously wrong"; "she was
            in bed and evidently in great pain"; "he was
            manifestly too important to leave off the guest list";
            "it is all patently nonsense"; "she has apparently
            been living here for some time"; "i thought he owned
            the property, but apparently not"; "you are plainly
            wrong"; "he is plain stubborn" syn: obviously, evidently,
             manifestly, patently, apparently, plain
     2: in a simple manner; without extravagance or embellishment;
        "she was dressed plainly"; "they lived very simply" syn:
        simply
see also:
obviously evidently manifestly patently apparently plain 
simply 

[3] : Moby Thesaurus II by Grady Ward, 1.0

106 moby thesaurus words for "plainly":
   all joking aside, alone, aloud, apparently, apprehensibly,
   articulately, artlessly, audibly, barely, bluffly, bluntly,
   broadly, brusquely, candidly, casually, clearly, coherently,
   commonly, commonplacely, comprehensibly, conspicuously, definitely,
   directly, discernibly, distinctly, en famille, evidently,
   exclusively, explicitly, expressly, familiarly, frankly, genuinely,
   glaringly, guilelessly, in all conscience, in all seriousness,
   in plain english, in plain terms, in plain words, informally,
   ingenuously, intelligibly, just, limpidly, lucidly, manifestly,
   markedly, matter-of-factly, merely, naturally, noticeably,
   observably, obviously, offhand, offhandedly, only, openheartedly,
   openly, ordinarily, out, out loud, outspokenly, palpably, patently,
   pellucidly, perceivably, perceptibly, perspicuously,
   plain-spokenly, point-blank, prominently, pronouncedly,
   prosaically, purely, recognizably, relaxedly, roundly,
   sans ceremonie, seeably, simply, simply and solely, sincerely,
   singly, solely, staringly, starkly, straightforwardly,
   to the point, unaffectedly, unambiguously, unassumingly,
   unceremoniously, unconcealedly, unconstrainedly, understandably,
   undisguisedly, unequivocally, unmistakably, unofficially,
   unreservedly, unrestrainedly, visibly, with clarity,
   with no nonsense, without ceremony

Plainly >> P Words
Plainly, definition of term: Plainly
plainly_pag1.html