Strengthening border means the world to a German (4)

I believe the answer is:

welt

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'strengthening border' is the definition.
'welt' can be an answer for 'border' (type of border on a garment). I'm unsure of the 'strengthening' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for welt that I've seen before include "Weal" , "High Ottoman official" , "Raised mark on the skin" , "After blow, Mark" , "narrow ridge" .)

I've seen this clue in The Guardian.

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