essential

The definition of essential is completely necessary or part of the basic nature of something.

(adjective)

See essential in Webster's New World College Dictionary

adjective

of or constituting the intrinsic, fundamental nature of something; basic; inherent: an essential difference
absolute; complete; perfect
absolutely necessary; indispensable; requisite
containing, or having the properties of, a concentrated extract of a plant, drug, food, etc.: an essential oil
Biochem. needed for life or health but not synthesized within the body, as an amino acid or vitamin that must be consumed

Origin: ME essencial < LL essentialis: see essence

noun

something necessary or fundamental; indispensable, inherent, or basic feature or principle

Related Forms:

See essential in American Heritage Dictionary 4

adjective

Constituting or being part of the essence of something; inherent.
Basic or indispensable; necessary: essential ingredients. See Synonyms at indispensable.
Medicine Of, relating to, or being a dysfunctional condition or a disease whose cause is unknown: essential hypertension.
Biochemistry Being a substance that is required for normal functioning but cannot be synthesized by the body and therefore must be included in the diet: essential amino acids.

noun