Pronunciation: (u-sen'shul),[key] —adj. 1. absolutely necessary; indispensable: Discipline is essential in an army. 2. pertaining to or constituting the essence of a thing.
3. noting or containing an essence of a plant, drug, etc.
4. being such by its very nature or in the highest sense; natural; spontaneous: essential happiness. 5. Math. a. (of a singularity of a function of a complex variable) noting that the Laurent series at the point has an infinite number of terms with negative powers.
b. (of a discontinuity) noting that the function is discontinuous and has no limit at the point. Cf. removable (def. 2).
—n. a basic, indispensable, or necessary element; chief point: Concentrate on essentials rather than details.