No longer changeable (3)
I believe the answer is:
set
'no longer changeable' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for set that I've seen before include "Determined or congealed" , "number of games" , "Class" , "group usually found together" , "Place - become rigid - adjust - group of tennis games - fixed - clique - fall beneath the horizon" .)