Medical Definition of essential
1: being, relating to, or containing an essence <an essential odor>
2: being a substance that is not synthesized by the body in a quantity sufficient for normal health and growth and that must be obtained from the diet <The body converts linoleic acid—an essential fatty acid that makes up 60 percent of corn oil—into arachidonic acid.—Janet Raloff, Science News, 24 June 1989>—see essential amino acid; compare nonessential
3: having no obvious or known cause : idiopathic <essential disease>
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