Crossword Genius

It's only natural that one should form an attachment (3)

Ross

I believe the answer is:

bur

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'attachment' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for bur that I've seen before include "Prickly seed case" , "Clinging seed case" , "small drill" , "sticker" , "Seed-case" .)

I've seen this clue in the Evening Standard.
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