In a cruel, cold, or merciless manner without compassion.
From 'hardhearted' plus the adverb suffix '-ly', which converts the adjective into an adverb describing how an action is performed or carried out.
Literature and history show that people who act hardheartedly often face narrative comeuppance—from Scrooge to modern villains, the hardheartedly cruel rarely end up happy, which says something about how morality shapes storytelling.
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