Definition of "Essential" :

noun: anything indispensable

"The essentials of the good life."

adjective: defining rights and duties as opposed to giving the rules by which rights and duties are established

adjective: basic and fundamental

"The essential feature."

adjective: of the greatest importance

adjective: absolutely necessary; vitally necessary

"Essential tools and materials."

adjective: being or relating to or containing the essence of a plant etc

"Essential oil."