Why is the ninth month called September?
mid-14c., "that is such by its essence," from Late Latin essentialis, from essentia (see essence). Meaning "pertaining to essence" is from late 14c., that of "constituting the essence of something" is from 1540s; that of "necessary" is from 1520s. Essentials "indispensable elements" is from early 16c. Related: Essentially.
essential es·sen·tial (ĭ-sěn'shəl)
Constituting or being part of the essence of something; inherent.
Basic or indispensable; necessary.
Of, relating to, or being a dysfunctional condition or a disease whose cause is unknown.
Of, relating to, or being a substance that is required for normal functioning but cannot be synthesized by the body and therefore must be included in the diet.
Something necessary or indispensable.