The Collaborative International Dictionary of English v.0.48:

Sufferer \Suf"fer*er\, n.
   1. One who suffers; one who endures or undergoes suffering;
      one who sustains inconvenience or loss; as, sufferers by
      poverty or sickness; men are sufferers by fire or by
      losses at sea.
      [1913 Webster]

   2. One who permits or allows.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sufferer
    n 1: a person suffering from an illness [syn: sick person,
         diseased person, sufferer]
    2: one who suffers for the sake of principle [syn: martyr,
       sufferer]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "sufferer":
   apoplectic, arthritic, case, consumptive, dyspeptic, epileptic,
   incurable, inpatient, invalid, martyr, object of compassion,
   outpatient, patient, poor devil, prey, rheumatic, shut-in,
   sick person, spastic, terminal case, the sick, valetudinarian,
   victim, wretch