Essential, a.
Etymology: [Cf. F. essentiel. See Essence.]
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.
2. Hence, really existing; existent. Is it true, that thou art but a a name, And no essential thing Webster (1623).
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.
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.
4 more senses
5. (Mus.)
Necessary; indispensable; -- said of those tones which constitute a chord, in distinction from ornamental or passing tones.
6. (Med.)
Idiopathic; independent of other diseases. 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.
1 other Webster entry under this spelling
Essential, n.
1. Existence; being. [Obs.] Milton.
2. That which is essential; first or constituent principle; as, the essentials or religion.
Shades of meaning
Fernald has no entry of its own for essential; he lists it under inherent, necessary, necessity, radical, real.
Where he writes about it:
That which is essential belongs to the essence of a thing, so that the thing can not exist in its completeness without it; that which is indispensable may be only an adjunct, but it is one that can not be spared; vigorous health is essential to an arctic explorer; warm clothing is indispensable. — from necessary
An essential is something, as a quality, or element, that belongs to the essence of something else so as to be inseparable from it in its normal condition, or in any complete idea or statement of it. — from necessity
The widely divergent senses in which the word radical is used, by which it can be at some time interchanged with any word in the above list, are all formed upon the one primary sense of having to do with or proceeding from the root (L. radix); a radical difference is one that springs from the root, and is thus constitutional, essential, fundamental, organic, original; a radical change is one that does not stop at the surface, but reaches down to the very root, and is entire, thorough, total; since the majority find superficial treatment of any matter the easiest and most comfortable, radical measures, which strike at the root of evil or need, are apt to be looked upon as extreme. — from radical