The Collaborative International Dictionary of English v.0.48:

Discernible \Dis*cern"i*ble\, a. [L. discernibilis.]
   Capable of being discerned by the eye or the understanding;
   as, a star is discernible by the eye; the identity of
   difference of ideas is discernible by the understanding.
   [1913 Webster]

         The effect of the privations and sufferings . . . was
         discernible to the last in his temper and deportment.
                                                  --Macaulay.

   Syn: Perceptible; distinguishable; apparent; visible;
        evident; manifest.
        [1913 Webster]

WordNet (r) 3.0 (2006):

discernible
    adj 1: perceptible by the senses or intellect; "things happen in
           the earth and sky with no discernible cause"; "the
           newspaper reports no discernible progress in the
           negotiations"; "the skyline is easily discernible even at
           a distance of several miles" [syn: discernible,
           discernable] [ant: indiscernible]
    2: capable of being perceived clearly; "an essay with a meaning
       that was not always discernible"
    3: capable of being seen or noticed; "a discernible change in
       attitude"; "a clearly evident erasure in the manuscript"; "an
       observable change in behavior" [syn: discernible,
       evident, observable]