In a wicked, evil, or deliberately cruel manner; with malicious intent.
Adverbial form created by adding '-ly' to 'blackhearted,' following standard English adverb formation rules. Allows the adjective quality to modify verbs and other adjectives.
Adding '-ly' to adjectives creates adverbs, but 'blackheartedly' is rarely used in modern English because 'wickedly' or 'cruelly' sound more natural—showing how some older compound words fade from everyday use even when grammatically valid.
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