The Collaborative International Dictionary of English v.0.48:

Pariah \Pa"ri*ah\, n. [From Tamil paraiyan, pl. paraiyar, one of
   the low caste, fr. parai a large drum, because they beat the
   drums at certain festivals.]
   [1913 Webster]
   1. One of an aboriginal people of Southern India, regarded by
      the four castes of the Hindus as of very low grade. They
      are usually the serfs of the Sudra agriculturalists. See
      Caste. --Balfour (Cyc. of India).
      [1913 Webster]

   2. An outcast; one despised by society.
      [1913 Webster]

   Pariah dog (Zool.), a mongrel race of half-wild dogs which
      act as scavengers in Oriental cities.

   Pariah kite (Zool.), a species of kite (Milvus govinda)
      which acts as a scavenger in India.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pariah
    n 1: a person who is rejected (from society or home) [syn:
         outcast, castaway, pariah, Ishmael]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "pariah":
   DP, Diogenes, Hieronymian, Hieronymite, Ishmael, Timon of Athens,
   alien, anchoress, anchorite, ascetic, bedridden invalid, case,
   castaway, character, cloistered monk, closet cynic, crackpot,
   crank, declasse, derelict, desert fathers, desert saints,
   displaced person, eccentric, eremite, evictee, exile, expatriate,
   expellee, fanatic, hermit, hermitess, hobo, homebody, invalid,
   isolationist, kook, leper, lone wolf, loner, marabout, maverick,
   meshuggenah, natural, nonconformist, nut, odd fellow, oddball,
   oddity, original, outcast, outcast of society, outcaste, outlaw,
   outsider, persona non grata, pillar saint, pillarist, queer duck,
   queer fish, queer specimen, rara avis, recluse, screwball,
   seclusionist, shut-in, social outcast, solitaire, solitary,
   solitudinarian, stay-at-home, stylite, tramp, type,
   unacceptable person, undesirable, untouchable, zealot