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ESSENTIAL, FUNDAMENTAL, VITAL, CARDINAL mean so important as to be indispensable.

ESSENTIAL implies belonging to the very nature of a thing and therefore being incapable of removal without destroying the thing itself or its character.

e.g. conflict is essential in drama

FUNDAMENTAL applies to something that is a foundation without which an entire system or complex whole would collapse.

e.g. fundamental principles of algebra

VITAL suggests something that is necessary to a thing's continued existence or operation.

e.g. cut off from vital supplies

CARDINAL suggests something on which an outcome turns or depends.

e.g. a cardinal rule in buying a home

1. absolutely necessary; extremely important:

«…にとって» 必要不可欠な, きわめて重要な, 必須の(crucial) «for, to»

e.g. with infinitive : it is essential to keep up-to-date records

e.g. fiber is an essential ingredient.

attributive fundamental or central to the nature of something or someone:

〖名詞の前で〗本質的な, 根本的な, 基本的な〈特徴･違いなど〉

e.g. the essential weakness of the plaintiff's case.

(of an amino acid or fatty acid) required for normal growth but not synthesized in the body and therefore necessary in the diet.

2. Medicine (of a disease) with no known external stimulus or cause; idiopathic:

〘医〙 本態性の, 特発性の

e.g. essential hypertension.

noun (usually essentials)

a thing that is absolutely necessary:

〖通例～s〗 必要不可欠な［絶対必要な］物

e.g. we had only the bare essentials in the way of gear.

(essentials) the fundamental elements or characteristics of something:

〖the ～s〗 最重要事項, 要点

e.g. he was quick to grasp the essentials of an opponent's argument.

essentiality |əˌsen(t)SHēˈalədē| noun

essentialness noun

Middle English (in the sense ‘in the highest degree’): from late Latin essentialis, from Latin essentia (see essence).