The Collaborative International Dictionary of English v.0.48:

Perceptible \Per*cep"ti*ble\ (p[~e]r*s[e^]p"t[i^]*b'l), a. [L.
   perceptibilis: cf. F. perceptible. See Perceive.]
   Capable of being perceived; cognizable; discernible;
   perceivable; large enough to be perceived; not so small as to
   be incapable of perception.
   [1913 Webster]

         With a perceptible blast of the air.     --Bacon.
   [1913 Webster] -- Per*cep"ti*ble*ness, n. --
   Per*cep"ti*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

perceptibly
    adv 1: in a noticeable manner; "he changed noticeably over the
           years" [syn: perceptibly, noticeably, observably]
           [ant: imperceptibly, unnoticeably]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "perceptibly":
   apparently, appreciably, clearly, conspicuously, definitely,
   discernibly, distinctly, evidently, explicitly, expressly,
   glaringly, manifestly, markedly, measurably, noticeably,
   observably, obviously, palpably, patently, perceivably, plainly,
   prominently, pronouncedly, recognizably, seeably, staringly,
   starkly, unconcealedly, undisguisedly, unmistakably, visibly,
   with clarity