1. (a.) Belonging to the essence, or that which makes an object, or class of objects, what it is.

2. (a.) Hence, really existing; existent.

3. (a.) Important in the highest degree; indispensable to the attainment of an object; indispensably necessary.

4. (a.) Containing the essence or characteristic portion of a substance, as of a plant; highly rectified; pure; hence, unmixed; as, an essential oil.

5. (a.) Necessary; indispensable; -- said of those tones which constitute a chord, in distinction from ornamental or passing tones.

6. (a.) Idiopathic; independent of other diseases.

ab ovo austere axiom bare bare necessities basal basic basilar bedrock bench mark brass tacks call for called for capital cardinal cardinal point center central chaste chief chief thing climax condition congenital connate constituent constitutional constitutive core cornerstone crisis critical point crux deep-seated demand demand for desideration desideratum element elemental elementary elixir essence essential facts essential matter essentials flower focal focus foremost fundamental gist gravamen great point gut heart high point homely homespun homogeneous hypostasis imperative important important thing inborn inbred indicated indispensable indivisible innate inner essence intrinsic irreducible irreductible irreplaceable issue kernel key keystone landmark leading life-and-death life-or-death main main point main thing marrow material material point meat mere milestone monolithic must must item necessaries necessary necessities necessitous necessity need need for needed needful nub nucleus nuts and bolts occasion of a piece of the essence of vital importance original part and parcel pith pivot plain postulate prerequirement prerequisite primal primary prime primitive principal principle pure pure and simple quid quiddity quintessence quintessential radical real issue required requirement requisite requisition right-hand rudiment rudimentary salient point sap severe simon-pure simple sine qua non single soul spare spirit stark stuff substance substantial substantive substantive point the bottom line the data the details the dope the facts the information the necessary the needful the nitty-gritty the particulars the picture the point the scoop the score the specifics the whole story turning point unadorned uncluttered underlying undifferenced undifferentiated unforgoable uniform vital want wanted