In a way that causes great surprise or amazement; surprisingly or shockingly.
From astound plus the suffix -ing (making a present participle) plus -ly (converting to adverb), creating an adverb that modifies verbs or adjectives to mean 'in an astounding manner'.
Astoundingly shows how English builds complexity by stacking suffixes—you can take a simple verb like 'stound,' add four morphemes, and describe something so surprising it leaves people speechless!
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