Firmly established (6)
'firmly established' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for vested that I've seen before include "This sort of interest means having a personal involvement" , "Robed; -- interest" , "Interests may be" , "Interest that is personal, often for financial gain" , "Like some interests" .)
'firmly established' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for entrenched that I've seen before include "Firmly established" , "as certain troops were on Somme?" , "Dug in" , "Difficult to shift" .)
(Other definitions for ensconced that I've seen before include "Settled comfortably" , "Safely established" , "Installed" , "in safe seat" .)