Both Uses

essential
in
The Marshall Plan Speech
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The truth of the matter is that Europe's requirements for the next three or four years of foreign food and other essential products — principally from America — are so much greater than her present ability to pay that she must have substantial additional help or face economic, social, and political deterioration of a very grave character.†

essential = necessary or important or relating to the basic nature of something
An essential part of any successful action on the part of the United States is an understanding on the part of the people of America of the character of the problem and the remedies to be applied.†
*

Definitions:

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