The Collaborative International Dictionary of English v.0.48:

Visible \Vis"i*ble\, a. [L. visibilis, fr. videre, visum, to
   see: cf. F. visible. See Vision.]
   1. Perceivable by the eye; capable of being seen;
      perceptible; in view; as, a visible star; the least spot
      is visible on white paper.
      [1913 Webster]

            Maker of heaven and earth, and of all things visible
            and invisible.                        --Bk. of Com.
                                                  Prayer.
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            Virtue made visible in outward grace. --Young.
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   2. Noticeable; apparent; open; conspicuous. --Shak.
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            The factions at court were greater, or more visible,
            than before.                          --Clarendon.
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   Visible church (Theol.), the apparent church of Christ on
      earth; the whole body of professed believers in Christ, as
      contradistinguished from the invisible, or real, church,
      consisting of sanctified persons.

   Visible horizon. Same as Apparent horizon, under
      Apparent.
      [1913 Webster] -- Vis"i*ble*ness, n. -- Vis"i*bly,
      adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

visibleness
    n 1: quality or fact or degree of being visible; perceptible by
         the eye or obvious to the eye; "low visibility caused by
         fog" [syn: visibility, visibleness] [ant:
         invisibility, invisibleness]