essential /is- or es-enˈshl/ adjective

1. Indispensable or important in the highest degree
2. Relating to, constituting or containing the essence
3. Necessary to the existence of a thing
4. Highly rectified
5. Pure
6. (of eg a disease) having no known cause

1. Something necessary
2. A leading principle

essenˈtialism noun

1. An educational theory that concentrates on teaching basic skills
2. A philosophical doctrine that distinguishes between the essence of material objects and their existence or appearance

essenˈtialist noun

essentiality /is-en-shi-alˈi-ti/ noun

1. The quality of being essential
2. An essential quality or element

essenˈtially adverb

essenˈtialness noun

essential minerals plural noun

Those whose presence is considered necessary to entitle a rock to the name it bears, opp to accessory minerals

essential oils plural noun

Oils which give plants their fragrance, used in cosmetics, toiletries, etc and in aromatherapy (also called ethereal oils or volatile oils)

essential organs plural noun (botany)

Stamens and carpels

in essence

Basically, fundamentally

of the essence

Of the utmost importance