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!