Squeak stopper (3)
I believe the answer is:
oil
'squeak stopper' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oil that I've seen before include "SECOND PART OF 23" , "Slippery liquid" , "Viscous substance as lubricant" , "Greasy liquid" , "What can be extracted" .)