c. 1300, astonien, "to stun, strike senseless," from Old French estoner "to stun, daze, deafen, astound," from Vulgar Latin *extonare, from Latin ex "out" (see ex-) + tonare "to thunder" (see thunder (n.)); so, literally "to leave someone thunderstruck." The modern form (influenced by English verbs in -ish, such as distinguish, diminish) is attested from 1520s. The meaning "amaze, shock with wonder" is from 1610s.
No wonder is thogh that she were astoned [Chaucer, "Clerk's Tale"]
Related: Astonished; astonishing.