essential

a. [ Cf. F. essentiel. See Essence. ] 1. Belonging to the essence, or that which makes an object, or class of objects, what it is. [ 1913 Webster ]

Majestic as the voice sometimes became, there was forever in it an essential character of plaintiveness. Hawthorne. [ 1913 Webster ]

2. Hence, really existing; existent. [ 1913 Webster ]

Is it true, that thou art but a name,
And no essential thing? Webster (1623). [ 1913 Webster ]

3. Important in the highest degree; indispensable to the attainment of an object; indispensably necessary. [ 1913 Webster ]

Judgment's more essential to a general
Than courage. Denham. [ 1913 Webster ]

How to live? -- that is the essential question for us. H. Spencer. [ 1913 Webster ]

4. Containing the essence or characteristic portion of a substance, as of a plant; highly rectified; pure; hence, unmixed; as, an essential oil. “Mine own essential horror.” Ford. [ 1913 Webster ]

5. (Mus.) Necessary; indispensable; -- said of those tones which constitute a chord, in distinction from ornamental or passing tones. [ 1913 Webster ]

6. (Med.) Idiopathic; independent of other diseases. [ 1913 Webster ]

Essential character (Biol.), the prominent characteristics which serve to distinguish one genus, species, etc., from another. --
Essential disease,
Essential fever (Med.), one that is not dependent on another. --
Essential oils (Chem.), a class of volatile oils, extracted from plants, fruits, or flowers, having each its characteristic odor, 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 from the fixed or nonvolatile. [ 1913 Webster ]