本質的, 實質的, 基本的, 提煉的, 精華的1. anything indispensable
同義詞：necessity, requirement, requisite, necessary
形容詞essential:
1. absolutely necessary; vitally necessary
同義詞：indispensable
2. basic and fundamental
3. of the greatest importance
同義詞：all-important, all important, crucial, of the essence
4. being or relating to or containing the essence of a plant etc
5. defining rights and duties as opposed to giving the rules by which rights and duties are established
同義詞：substantive
6. absolutely required and not to be used up or sacrificed
