Role played by tradition (4)
I believe the answer is:
lore
'tradition' is the definition.
(I know that lore is a type of tradition)
'role played' is the wordplay.
'played' indicates anagramming the letters (letters playing around).
'role' anagrammed gives 'LORE'.
'by' is the link.
(Other definitions for lore that I've seen before include "Folk knowledge" , "Role for learning" , "Role for tradition" , "Tales of old" , "Traditional knowledge" .)