The Collaborative International Dictionary of English v.0.48:

Limbo \Lim"bo\ (l[i^]m"b[-o]), Limbus \Lim"bus\ (l[i^]m"b[u^]s),
   n. [L. limbus border, edge in limbo on the border. Cf. Limb
   border.]
   1. (Scholastic Theol.) An spiritual region where certain
      classes of souls were supposed to await the last judgment.
      [1913 Webster]

            As far from help as Limbo is from bliss. --Shak.
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            A Limbo large and broad, since called
            The Paradise of fools.                --Milton.
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   Note: The limbus patrum was considered as a place for the
         souls of good men who lived before the coming of our
         Savior. The limbus infantium was said to be a similar
         place for the souls of unbaptized infants. To these was
         added, in the popular belief, the limbus fatuorum, or
         fool's paradise, regarded as a receptacle of all vanity
         and nonsense.
         [1913 Webster]

   2. Hence: Any real or imaginary place of restraint or
      confinement; a prison; as, to put a man in limbo.
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   3. Hence: A state of waiting, or uncertainty, in which final
      judgment concerning the outcome of a decision is
      postponed, perhaps indefinitely; neglect for an indefinite
      time; as, the proposal was left in limbo while opponents
      and proponents refused to compromise.
      [PJC]

   4. (Anat.) A border or margin; as, the limbus of the cornea.
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WordNet (r) 3.0 (2006):

limbus
    n 1: a border or edge of any of various body parts distinguished
         by color or structure