Know how to use "fewer" and "less"? Find out.
c.1300, astonien, from Old French estoner "to stun, daze, deafen, astound," from Vulgar Latin *extonare, from Latin ex- "out" + tonare "to thunder" (see thunder); so, literally "to leave someone thunderstruck." The modern form (influenced by English verbs in -ish, e.g. distinguish, diminish) is attested from c.1530.
No wonder is thogh that she were astoned [Chaucer, "Clerk's Tale"]Related: Astonished; astonishing; astonishingly.