To stun or shock someone so much that they can't think or move properly.
From Middle English astonen, derived from Old French estonner (to stun), from Vulgar Latin extonare combining ex- (out) and tonare (to thunder). The meaning evolved from the literal shock of thunder to any shocking or stunning event.
This is an archaic cousin of the modern word 'astonish'—both come from the idea of being struck by thunder so hard you lose your senses. Medieval people thought thunder was literally stunning.
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