essential

(noun) anything indispensable. Synonyms: necessity, requirement, requisite, necessary. Examples: "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."

(adj) absolutely necessary; vitally necessary. Synonyms: indispensable. Examples: "Essential tools and materials." "Funds essential to the completion of the project." "An indispensable worker."

(adj) basic and fundamental. Synonyms: essential (vs. inessential). Example: "The essential feature."

(adj) of the greatest importance. Synonyms: all-important(prenominal), all important(predicate), crucial, of the essence(predicate). Examples: "The all-important subject of disarmament." "Crucial information." "In chess cool nerves are of the essence."

(adj) being or relating to or containing the essence of a plant etc. Example: "Essential oil."

(adj) defining rights and duties as opposed to giving the rules by which rights and duties are established. Synonyms: substantive (vs. adjective). Example: "Substantive law."