Source : Webster's Revised Unabridged Dictionary (1913)

Nimbus \Nim"bus\, n.; pl. L. {Nimbi}, E. {Nimbuses}. [L., a rain
   storm, a rain cloud, the cloudshaped which enveloped the gods
   when they appeared on earth.]
   1. (Fine Arts) A circle, or disk, or any indication of
      radiant light around the heads of divinities, saints, and
      sovereigns, upon medals, pictures, etc.; a halo. See
      {Aureola}, and {Glory}, n., 5.

   Note: ``The nimbus is of pagan origin.'' ``As an atribute of
         power, the nimbus is often seen attached to the heads
         of evil spirits.'' --Fairholl.

   2. (Meteor.) A rain cloud; one of the four principal
      varieties of clouds. See {Cloud}.

Source : WordNet®

nimbus
     n 1: a dark gray cloud bearing rain [syn: {nimbus cloud}, {rain
          cloud}]
     2: an indication of radiant light drawn around the head of a
        saint [syn: {aura}, {aureole}, {halo}, {glory}, {gloriole}]
     [also: {nimbi} (pl)]

nimbi
     See {nimbus}