the.com/hailstorm

means A storm in which lumps of ice, called hailstones, fall from the sky, sometimes hard enough to dent cars and batter crops.

from A plain compound of two old English words: 'hail' (Old English 'hægl', the frozen pellets, with relatives across the Germanic languages like German 'Hagel') stitched onto 'storm' (Old English 'storm', a tumult or tempest, also widely Germanic). So the name does exactly what it says — a storm made of hail — no mystery, just two ancient weather-words shaken together.