形容词 “essential” 既可以表示 “必要的，不可或缺的”，也可以表示 “本质的，根本的”。此外，“essential” 还可作名词，常以复数形式 “essentials” 出现，表示 “必需品” 或 “要素，要点”。

用法总结

1 “Essential” 作形容词用，可以表示 “必要的，不可或缺的”。

We can't live without water. It's essential.

Previous work experience is essential if you'd like to apply for this job.

2 形容词 “essential” 也可以表示 “本质的，根本的，（人或事物最重要的）基本特征”。

It's a beautiful old house. We don't want to change its essential character.

This company has failed due to its essential misconception about the global market.

3 “Essential” 可作可数名词用，表示 “必需品，不可缺少的东西”，常以复数形式 “essentials” 出现。

When we go camping, we only take a few essentials with us.

They are calling for donations of winter essentials like blankets and warm clothing. 

4 可数名词 “essential” 还可以表示 “要素，要点”。在表达这个意思时通常用其复数形式 “essentials”，并在前面加 “the”， 后面跟 “of”，即 “the essentials of”. 

Make sure you understand all the essentials of a valid contract before signing one.

Now you have all the essentials of the word 'essential'.