hailstone(n = noun.substance) - small pellet of ice that falls during a hailstorm;
is a kind of ice, water ice
is a part of hail

   A single particle of ice falling from a cloud; a frozen raindrop; a pellet of hail. [1913 Webster]

hailstone, n. a pellet of hail.

N  cold, coldness, frigidity, inclemency, fresco, winter, depth of winter, hard winter, Siberia, Nova Zembla, wind- chill factor, ice, snow, snowflake, snow crystal, snow drift, sleet, hail, hailstone, rime, frost, hoar frost, white frost, hard frost, sharp frost, barf, glaze, lolly, icicle, thick-ribbed ice, fall of snow, heavy fall, iceberg, icefloe, floe berg, glacier, nev_ee, serac, pruina, freezing mixture, dry ice, liquid nitrogen, liquid helium, chilliness, chill, shivering, goose skin, horripilation, rigor, chattering of teeth, numbness, frostbite, cold, cool, chill, chilly, icy, gelid, frigid, algid, fresh, keen, bleak, raw, inclement, bitter, biting, niveous, cutting, nipping, piercing, pinching, clay-cold, starved, chilled to the bone, shivering, aguish, transi de froid, frostbitten, frost-bound, frost-nipped, cold as a stone, cold as marble, cold as lead, cold as iron, cold as a frog, cold as charity, cold as Christmas, cool as a cucumber, cool as custard, icy, glacial, frosty, freezing, pruinose, wintry, brumal, hibernal, boreal, arctic, Siberian, hyemal, hyperborean, hyperboreal, icebound, frozen out, unwarmed, unthawed, lukewarm, tepid, isocheimal, isocheimenal, isocheimic, frozen, numb, frost-bitten, coldly, bitterly, pierre fendre.