Some useful traditions for extremist (5)
I believe the answer is:
ultra
'extremist' is the definition.
(synonyms)
'some useful traditions for' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ULTRA' can be found hidden inside 'useful traditions for'.
(Other definitions for ultra that I've seen before include "Prefix meaning beyond or extremely" , "Above, beyond, super" , "(One who is) extreme (in eg political opinion)" , "Extreme - extremist" , "Project started at Bletchley Park in 1939 to break the Enigma code" .)