Plural of coot; waterbirds with dark plumage and a distinctive white facial patch, or slang for old people.
From Middle Dutch 'coot' or Middle Low German 'kute,' ultimately from an imitative origin mimicking the bird's harsh call.
Coots are famously aggressive birds that will attack each other and other waterfowl, so calling someone an old coot suggests they're cranky and combative—which is probably why the slang stuck around.
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