In a way that is extremely frightening or horrifying; with intense fear-inducing quality.
Adverbial form of 'bloodcurdling' with suffix '-ly' (Old English -lice); follows standard adverb formation from adjectives to modify verbs and other descriptors.
Adding '-ly' to adjectives to make adverbs is so common we barely notice it, but 'bloodcurdlingly' is actually quite rare in modern writing because we now prefer simpler words like 'horrifyingly'—it's a relic of Victorian dramatic language.
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