Fulcrum; turn (5)
I believe the answer is:
pivot
I believe this is a double definition.
'fulcrum' is the first definition.
(I've seen this in another clue)
'turn' is the second definition.
(I know that pivot is a type of turn)
(Other definitions for pivot that I've seen before include "Central point on which things turn" , "Central point around which mechanism moves" , "Key figure" , "Turning pin" , "Centre point" .)