Pioneered (3)
I believe the answer is:
led
'pioneered' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for led that I've seen before include "Went first to show the way" , "was in the van" , "Took by the hand and showed the way" , "Something emitting light" , "Guided; small light" .)