Source : Webster's Revised Unabridged Dictionary (1913)

Downpour \Down"pour`\, n.
   A pouring or streaming downwards; esp., a heavy or continuous
   shower.

Source : WordNet®

downpour
     n : a heavy rain [syn: {cloudburst}, {deluge}, {waterspout}, {torrent},
          {pelter}, {soaker}]