All 5 Uses

essential
in
Flags of Our Fathers
(Auto-generated)

Shared responsibility—an abiding sense of the unit—is essential to survival in combat.†
Chpt 2.

essential = necessary or important or relating to the basic nature of something
His attitude, his friend recalled, was essentially: I'm goin' in anyway.†
Chpt 4. *

essentially = basically (in all important respects; or relating to the basic nature of something)
But now they began to understand that the rifle was the essential weapon of combat in this war.†
Chpt 5.

essential = necessary or important or relating to the basic nature of something
Third, because the replacement flagraising was essentially a nonevent, little was said about it.†
Chpt 12.

essentially = basically (in all important respects; or relating to the basic nature of something)
War bonds were the chief mechanism for this volunteer funding, essentially a citizen's loan to the government.†
Chpt 15.

Definitions:

(1) (essential)
necessary or important; or a basic and defining part of something
(2) (meaning too rare to warrant focus)