Influential expert (4)
I believe the answer is:
guru
'influential expert' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for guru that I've seen before include "Hindu or Sikh religious teacher or leader" , "Wise leader" , "Swami" , "Name given to the each of the first ten leaders of the Sikh religion" , "Hindu or Buddhist spiritual teacher" .)