Belonging to the essence, or that which makes
an object, or class of objects, what it is.
Hence, really existing;
existent.
Important in the highest degree;
indispensable to the attainment of an object; indispensably
necessary.
Containing the essence or characteristic
portion of a substance, as of a plant; highly rectified; pure; hence,
unmixed; as, an essential oil.
Necessary; indispensable; --
said of those tones which constitute a chord, in distinction from
ornamental or passing tones.
Idiopathic; independent of
other diseases.
In celebration of Noah Webster's Birthday (October 16, 2009), we have prepared an updated website. 
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