ˈkɹuː.ʃəl ɪˈsɛn.ʃəl ɪˈsɛn.ʃəl ɪndɪˈspɛnsəbəl ˈnɛsəˌsɛɹi ˈnɛsəsɹɪ nɪˈsɛsəti ɹɪˈkwʌɪəm(ə)nt ɹɪˈkwaɪɹmənt ɹɪˈkwɪzɪt ˈɹɛkwɪzɪt ˈsʌbstəntɪv defining rights and duties as opposed to giving the rules by which rights and duties are established substantive law basic and fundamental the essential feature of the greatest importance the all-important subject of disarmament crucial information in chess cool nerves are of the essence absolutely necessary; vitally necessary essential tools and materials funds essential to the completion of the project an indispensable worker being or relating to or containing the essence of a plant etc essential oil anything indispensable food and shelter are necessities of life the essentials of the good life allow farmers to buy their requirements under favorable conditions a place where the requisites of water fuel and fodder can be obtained