bur

also burr (bûr)

1. a. A rough prickly husk or covering surrounding the seeds or fruits of plants such as the chestnut or the burdock.
   b. A plant producing such husks or coverings.
2. A persistently clinging or nettlesome person or thing.
3. A rough protuberance, especially a burl on a tree.
4. Any of various rotary cutting tools designed to be attached to a drill.

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