Vaulter's aid (4)
I believe the answer is:
pole
'vaulter's aid' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pole that I've seen before include "Punt propeller" , "European; measure of length" , "This position is favourable in motor race" , "One of two opposites" , "National from east" .)