The Collaborative International Dictionary of English v.0.48:

Nobody \No"bod*y\, n.; pl. Nobodies. [No, a. + body.]
   1. No person; no one; not anybody.
      [1913 Webster]

   2. Hence: A person of no influence or importance; an
      insignificant or contemptible person. [Colloq.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

nobody
    n 1: a person of no influence [syn: cipher, cypher,
         nobody, nonentity]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "nobody":
   a nobody, a nothing, cipher, common man, dud, dummy, figurehead,
   hollow man, insignificancy, jackstraw, lay figure, lightweight,
   little fellow, little guy, man of straw, mediocrity, nary one,
   nebbish, never a one, no man, no one, nobody on earth,
   nobody one knows, nobody present, nonentity, not a soul, not one,
   nothing, nullity, obscurity, pip-squeak, punk, puppet, pushover,
   runt, scrub, shrimp, small fry, small potato, small potatoes,
   squirt, squit, thing of naught, trifle, unknown, whiffet,
   whippersnapper, zero, zilch