The Collaborative International Dictionary of English v.0.48:

Plague \Plague\, n. [L. plaga a blow, stroke, plague; akin to
   Gr. ?, fr. ? to strike; cf. L. plangere to strike, beat. Cf.
   Plaint.]
   1. That which smites, wounds, or troubles; a blow; a
      calamity; any afflictive evil or torment; a great trail or
      vexation. --Shak.
      [1913 Webster]

            And men blasphemed God for the plague of hail.
                                                  --Wyclif.
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            The different plague of each calamity. --Shak.
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   2. (Med.) An acute malignant contagious fever, that often
      prevails in Egypt, Syria, and Turkey, and has at times
      visited the large cities of Europe with frightful
      mortality; hence, any pestilence; as, the great London
      plague. "A plague upon the people fell." --Tennyson.
      [1913 Webster]

   Cattle plague. See Rinderpest.

   Plague mark, Plague spot, a spot or mark of the plague;
      hence, a token of something incurable.
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The Collaborative International Dictionary of English v.0.48:

Plague \Plague\, v. t. [imp. & p. p. Plagued; p. pr. & vb. n.
   Plaguing.]
   1. To infest or afflict with disease, calamity, or natural
      evil of any kind.
      [1913 Webster]

            Thus were they plagued
            And worn with famine.                 --Milton.
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   2. Fig.: To vex; to tease; to harass.
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            She will plague the man that loves her most.
                                                  --Spenser.
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   Syn: To vex; torment; distress; afflict; harass; annoy;
        tease; tantalize; trouble; molest; embarrass; perplex.
        [1913 Webster]

WordNet (r) 3.0 (2006):

plague
    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 swarm of insects that attack plants; "a plague of
       grasshoppers" [syn: infestation, plague]
    4: any large scale calamity (especially when thought to be sent
       by God)
    5: an annoyance; "those children are a damn plague"
    v 1: cause to suffer a blight; "Too much rain may blight the
         garden with mold" [syn: blight, plague]
    2: annoy continually or chronically; "He is known to harry his
       staff when he is overworked"; "This man harasses his female
       co-workers" [syn: harass, hassle, harry, chivy,
       chivvy, chevy, chevvy, beset, plague, molest,
       provoke]

The Devil's Dictionary (1881-1906):

PLAGUE, n.  In ancient times a general punishment of the innocent for
admonition of their ruler, as in the familiar instance of Pharaoh the
Immune.  The plague as we of to-day have the happiness to know it is
merely Nature's fortuitous manifestation of her purposeless
objectionableness.