WordNet (r) 3.0 (2006):

someone
    n 1: a human being; "there was too much for one person to do"
         [syn: person, individual, someone, somebody,
         mortal, soul]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "someone":
   Adamite, being, body, cat, chap, character, creature, customer,
   duck, earthling, fellow, groundling, guy, hand, head, homo, human,
   human being, individual, joker, life, living soul, man, mortal,
   nose, one, party, person, personage, personality, single, somebody,
   soul, tellurian, terran, worldling