Source : Webster's Revised Unabridged Dictionary (1913)

Thundercloud \Thun"der*cloud`\, n.
   A cloud charged with electricity, and producing lightning and
   thunder.

Source : WordNet®

thundercloud
     n : a dark cloud of great vertical extent charged with
         electricity; associated with thunderstorms [syn: {cumulonimbus},
          {cumulonimbus cloud}]