Plural of arbor; structures with a frame covered in climbing plants, or axles that support rotating parts in machinery.
From Latin 'arbor' meaning tree, borrowed into English where it developed both a horticultural meaning (a tree-like structure) and a mechanical meaning (rotating shaft), showing how one word evolved multiple technical uses.
A garden arbor and a machine arbor are totally different things—but they share the name because medieval engineers named wheel-shafts after trees since they're the central spinning part, just like a tree's trunk is central to the forest!
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