Source : Webster's Revised Unabridged Dictionary (1913)

Pest \Pest\, n. [L. pestis: cf. F. peste.]
   1. A fatal epidemic disease; a pestilence; specif., the
      plague.

            England's sufferings by that scourge, the pest.
                                                  --Cowper.

   2. Anything which resembles a pest; one who, or that which,
      is troublesome, noxious, mischievous, or destructive; a
      nuisance. ``A pest and public enemy.'' --South.

Source : WordNet®

pest
     n : a persistently annoying person [syn: {blighter}, {cuss}, {pesterer},
          {gadfly}]