Source : Webster's Revised Unabridged Dictionary (1913)

Invisible \In*vis"i*ble\, a. [F. invisible, L. invisibilis. See
   {In-} not, and {Visible}.]
   Incapable of being seen; not perceptible by vision; not
   visible.

         To us invisible, or dimly seen In these thy lowest
         works.                                   --Milton.

   {Invisible bird} (Zo["o]l.), a small, shy singing bird
      ({Myadestes sibilons}), of St. Vincent Islands.

   {Invisible green}, a very dark shade of green, approaching to
      black, and liable to be mistaken for it.

Invisible \In*vis"i*ble\, n.
   1. An invisible person or thing; specifically, God, the
      Supreme Being.

   2. A Rosicrucian; -- so called because avoiding declaration
      of his craft. [Obs.]

   3. (Eccl. Hist.) One of those (as in the 16th century) who
      denied the visibility of the church. --Shipley.

Source : WordNet®

invisible
     adj 1: impossible or nearly impossible to see; imperceptible by the
            eye; "the invisible man"; "invisible rays"; "an
            invisible hinge"; "invisible mending" [syn: {unseeable}]
            [ant: {visible}]
     2: not prominent or readily noticeable; "he pushed the string
        through an inconspicuous hole"; "the invisible man" [syn:
        {inconspicuous}] [ant: {conspicuous}]