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Funny you should ask that...
I always knew Tweed was the old Brittonic word for border, as this sepearates England Scotland so makes sense...

However I found out that ...

Tweed got its name by accident in 1826 in Hawick, when a merchant's label on a shipment of wool tweel (the Scottish term for twill) bound for a London milliner was misread and confused with the moniker of the nearby River Tweed.

Who knew!