adj. & n.
adj. 1 absolutely necessary; indispensable. 2 fundamental, basic. 3 of or constituting the essence of a person or thing. 4 (of a disease) with no known external stimulus or cause; idiopathic.
n. (esp. in pl.) a basic or indispensable element or thing. essential element any of various elements required by living organisms for normal growth. essential oil a volatile oil derived from a plant etc. with its characteristic odour. essentiality n. essentially adv. essentialness n.
[ ME f. LL essentialis (as ESSENCE) ]