To fill with sorrow; to make sad or mournful.
From 'sorrow' plus the prefix 'en-' (meaning 'to cause to be' or 'to fill with'). 'Sorrow' comes from Old English 'sorg,' related to German 'Sorge' (care/worry).
The prefix 'en-' in English is like a magical intensifier—'sorrow' is already sad, but 'ensorrow' means to *fill something with* that sadness, the same way 'enlarge' means to make large in a more active sense than just 'large.'
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