The Collaborative International Dictionary of English v.0.48:

Pestilence \Pes"ti*lence\, n. [F. pestilence, L. pestilentia.
   See Pestilent.]
   1. Specifically, the disease known as the plague; hence, any
      contagious or infectious epidemic disease that is virulent
      and devastating.
      [1913 Webster]

            The pestilence that walketh in darkness. --Ps. xci.
                                                  6.
      [1913 Webster]

   2. Fig.: That which is pestilent, noxious, or pernicious to
      the moral character of great numbers.
      [1913 Webster]

            I'll pour this pestilence into his ear. --Shak.
      [1913 Webster]

   Pestilence weed (Bot.), the butterbur coltsfoot (Petasites
      vulgaris), so called because formerly considered a remedy
      for the plague. --Dr. Prior.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pestilence
    n 1: a serious (sometimes fatal) infection of rodents caused by
         Yersinia pestis and accidentally transmitted to humans by
         the bite of a flea that has bitten an infected animal [syn:
         plague, pestilence, pest, pestis]
    2: any epidemic disease with a high death rate [syn: plague,
       pestilence, pest]
    3: a pernicious and malign influence that is hard to get rid of;
       "racism is a pestilence at the heart of the nation";
       "according to him, I was the canker in their midst" [syn:
       pestilence, canker]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "pestilence":
   Black Death, affliction, ambulatory plague, bane, black death,
   black plague, blight, bubonic plague, bugbear, burden, calamity,
   cancer, canker, cellulocutaneous plague, crushing burden, curse,
   death, defervescing plague, destruction, disease, epidemic,
   epiphytotic, epizootic, evil, glandular plague, grievance, harm,
   hemorrhagic plague, infliction, larval plague, murrain, nemesis,
   open wound, pandemia, pandemic, pest, pesthole, plague,
   plague spot, pneumonic plague, premonitory plague, running sore,
   scourge, septicemic plague, siderating plague, thorn, torment,
   tuberculosis, vexation, visitation, white plague, woe