Chief warning the majority (8)
I believe the answer is:
foremost
'chief' is the definition.
(thesaurus)
'warning the majority' is the wordplay.
'warning' becomes 'fore' (I've seen this in other clues).
'the majority' becomes 'most' (I've seen this before).
'fore'+'most'='FOREMOST'
(Other definitions for foremost that I've seen before include "First in time, place or order" , "Most prominent" , "premier" , "van" , "'Leading, best (8)'" .)