Tunnels or holes dug in the ground by small animals, or the shelters animals make underground.
From Old English 'burg' meaning 'fortress,' which evolved to mean small fortified structures, then animal tunnels. Related to 'borough' and 'bury.'
The word 'burrow' connects to 'borough' and 'burgher'—a fortress, a town, and a rabbit hole all share the same ancient root because they're all about having your own enclosed, protected space!
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