The Collaborative International Dictionary of English v.0.48:

Leper \Lep"er\ (l[e^]p"[~e]r), n. [OE. lepre leprosy, F.
   l[`e]pre, L. leprae, lepra, fr. Gr. le`pra, fr. lepro`s
   scaly, fr. le`pos scale, le`pein to peel.]
   A person affected with leprosy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

leper
    n 1: a person afflicted with leprosy [syn: leper, lazar]
    2: a pariah who is avoided by others

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "leper":
   DP, Ishmael, castaway, declasse, derelict, displaced person,
   evictee, exile, expatriate, expellee, outcast, outcast of society,
   outcaste, outlaw, pariah, persona non grata, social outcast,
   unacceptable person, undesirable, untouchable