Popular brand set in stone (9)
I believe the answer is:
excalibur
This could be a double definition.
'popular brand' is the first definition.
The definition suggests a singular noun which matches the answer.
'stone' is the second definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?
'set in' is the link.
(Other definitions for excalibur that I've seen before include "King Arthur's magical sword" , "The legendary sword of King Arthur" , "King Arthur's magic sword" , "Legendary weapon" , "Steel flourished years ago" .)