From an alteration (due to words ending in
-ish:
abolish,
banish,
cherish,
establish,
furnish, etc.) of earlier
astony,
astone,
aston,
astun (“to astonish, confound, stun”), from Middle English
astonien,
astunien,
astonen,
astunen,
astounen (“to astound, stun, astonish”), from Old English
*āstunian, from
ā- (perfective prefix) +
stunian (“to make a loud sound, crash, resound, roar, bang, dash, impinge, knock, confound, astonish, stupefy”), from
Proto-Germanic *stunōną (“to sound, crash, bang, groan”), from
Proto-Indo-European *(s)ten-,
*(s)ton- (“to thunder, roar, groan”), equivalent to
a- +
stun. Compare
German erstaunen (“to astonish, amaze”). Influenced by Old French
estoner,
estuner,
estonner (“to stun”), either from an assumed
Latin *extonare, or from Old
Frankish *stunen (“to stun”), related to Middle High German
stunen (“to knock, strike, stun”) and thus also to the Old English word above.