In a way that surprises or shocks someone greatly; extremely surprisingly.
From 'astonish,' which came from Old French 'astonir,' meaning to stun or knock senseless. The '-ing' makes it a present participle and '-ly' converts it to an adverb describing the manner of the action.
Astonish literally means to 'stun like thunder'—it comes from the same root as 'thunder,' which is why being astonished feels like being struck by something sudden and powerful. The word captures the physical experience of surprise as much as the mental one.
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