- essential [ə sen′shəl, isen′shəl]adj.[ME essencial < LL essentialis: see ESSENCE]1. of or constituting the intrinsic, fundamental nature of something; basic; inherent [an essential difference]2. absolute; complete; perfect3. absolutely necessary; indispensable; requisite4. containing, or having the properties of, a concentrated extract of a plant, drug, food, etc. [an essential oil]5. Biochem. needed for life or health but not synthesized within the body, as an amino acid or vitamin that must be consumedn.something necessary or fundamental; indispensable, inherent, or basic feature or principleessentiallyadv.SYN.- ESSENTIAL, in strict usage, is applicable to that which constitutes the absolute essence or the fundamental nature of a thing and therefore must be present for the thing to exist, function, etc. [food is essential to life ]; an INDISPENSABLE person or thing cannot be done without if the specified or implied purpose is to be achieved; REQUISITE is applied to that which is required by the circumstances or for the purpose and generally suggests a requirement that is imposed externally rather than an inherent need [the requisite experience for a position ]; NECESSARY implies a pressing need but does not always connote absolute indispensability
English World dictionary. V. Neufeldt. 2014.