en·trench / enˈtrench/ (also dated in·trench) • v. [tr.] (often be entrenched) establish (an attitude, habit, or belief) so firmly that change is very difficult or unlikely: ageism is entrenched in our society. ∎  establish (a person or their authority) in a position of great strength or security. ∎  apply extra legal safeguards to (a right, esp. a constitutional right, guaranteed by legislation). ∎  establish (a military force, camp, etc.) in trenches or other fortified positions.DERIVATIVES: en·trench·ment n.

entrench, intrench place within a trench XVI; encroach (upon) XVII. f. EN-1, IN-1 + TRENCH.
Hence entrenchment XVI.