1. Belonging to the essence, or that which makes an object, or class of objects, what it is. Majestic as the voice sometimes became, there was forever in it an essential character of plaintiveness. (Hawthorne)
3. Important in the highest degree; indispensable to the attainment of an object; indispensably necessary. Judgment's more essential to a general Than courage. (Denham) How to live? that is the essential question for us. (H. Spencer)
(Science: biology) essential character, a class of volatile oils, extracted from plants, fruits, or flowers, having each its characteristic odour, and hot burning taste. They are used in essences, perfumery, etc, and include many varieties of compounds; as lemon oil is a terpene, oil of bitter almonds an aldehyde, oil of wintergreen an ethereal salt, etc.; called also volatile oils in distinction f 42f rom the fixed or nonvolatile.