Symbol of some nationalism that could be anti-brain (9)
I believe the answer is:
britannia
'symbol of some nationalism' is the definition.
The definition suggests a singular noun which matches the answer.
'could be anti-brain' is the wordplay.
'could be' indicates an anagram.
'anti'+'brain'='antibrain'
'antibrain' anagrammed gives 'BRITANNIA'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for britannia that I've seen before include "In song, she used to rule the waves" , "our sitting representative" , "National representative" , "Female personification of Britain" , "Figure on some British coins" .)