The Collaborative International Dictionary of English v.0.48:

Outsider \Out`sid"er\, n.
   1. One not belonging to the concern, institution, party,
      etc., spoken of; one disconnected in interest or feeling.
      [Recent] --A. Trollope.
      [1913 Webster]

   2. A locksmith's pinchers for grasping the point of a key in
      the keyhole, to open a door from the outside when the key
      is inside.
      [1913 Webster]

   3. A horse which is not a favorite in the betting. [Cant]
      [1913 Webster]

WordNet (r) 3.0 (2006):

outsider
    n 1: someone who is excluded from or is not a member of a group
         [syn: foreigner, outsider]
    2: a contestant (human or animal) not considered to have a good
       chance to win