Entry 1 sense Webster, 1913 Hailstone /(-stōn`)/ · Hail·stone · IPA /ˈheɪlstoʊn/ 01 n. A single particle of ice falling from a cloud; a frozen raindrop; a pellet of hail. 1. A single particle of ice falling from a cloud; a frozen raindrop; a pellet of hail.