a potato, or a digging tool with a flat blade used for loosening soil.
Originally referred to a digging tool (from unknown origin, possibly variant of 'spade'), and around the 1800s came to mean potato, perhaps because the tool was used to dig them up.
The word 'spud' for potato is pretty mysterious—nobody knows for sure why it stuck, but it became super popular slang in the 1900s and is one of those casual words that stuck around forever in English.
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