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]