An exclamation of regret, sorrow, or disappointment, now mostly used in old-fashioned or humorous contexts.
From Middle English 'alak' possibly from Old Norse. It's related to 'alas' and was commonly used in Shakespearean English, appearing frequently in his plays as a cry of woe.
Alack is essentially dead—it survives now only in Shakespeare quizzes and fantasy novels—which makes it a perfect example of how thousands of words are constantly 'dying' in languages as speakers find new ways to express emotions.
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