Noah Webster's Dictionary (n.) A sudden copious rainfall, as the whole cloud had been precipitated at once.

Multi-Version Concordance Cloud-burst (1 Occurrence) Isaiah 30:30 And the Lord will send out the sound of his great voice, and they will see his arm stretched out, with the heat of his wrath, and the flame of a burning fire; with a cloud-burst, and storm, and a rain of ice. (BBE)