In a way that causes intense sadness or emotional pain; in a manner that deeply distresses or upsets someone.
From 'heartbreak' (heart + break) + '-ing' + '-ly' (Old English adverbial suffix). The adverbial form evolved to describe how actions or situations are executed in a heartbreaking manner.
The word 'heartbreak' didn't exist in English before the 1500s—before that, people described sadness without this specific heart-focused term, suggesting that how we label emotions actually changes how we experience them.
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