In a way that shows an eager desire to hurt people or cause violence; cruelly and savagely.
From 'bloodthirsty' plus the adverb-forming suffix '-ly,' which converts adjectives into adverbs describing manner or action. This form dates to the 16th century.
Adverbs ending in '-ly' often sound intensely serious and descriptive—'bloodthirstily' is almost theatrical, which is why it appears so often in historical novels and dramatic literature about villains plotting their cruel deeds.
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