Source : Webster's Revised Unabridged Dictionary (1913)

Essential \Es*sen"tial\, a. [Cf. F. essentiel. See {Essence}.]
   1. Belonging to the essence, or that which makes an object,
      or class of objects, what it is.

            Majestic as the voice sometimes became, there was
            forever in it an essential character of
            plaintiveness.                        --Hawthorne.

   2. Hence, really existing; existent.

            Is it true, that thou art but a a name, And no
            essential thing?                      --Webster
                                                  (1623).

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

            Judgment's more essential to a general Than courage.
                                                  --Denham.

            How to live? -- that is the essential question for
            us.                                   --H. Spencer.

   4. Containing the essence or characteristic portion of a
      substance, as of a plant; highly rectified; pure; hence,
      unmixed; as, an essential oil. ``Mine own essential
      horror.'' --Ford.

Source : WordNet®

essential
     n : anything indispensable; "food and shelter are necessities of
         life"; "the essentials of the good life"; "allow farmers
         to buy their requirements under favorable conditions"; "a
         place where the requisites of water fuel and fodder can
         be obtained" [syn: {necessity}, {requirement}, {requisite},
          {necessary}] [ant: {inessential}]

essential
     adj 1: absolutely necessary; vitally necessary; "essential tools
            and materials"; "funds essential to the completion of
            the project"; "an indispensable worker" [syn: {indispensable}]
     2: basic and fundamental; "the essential feature" [ant: {inessential}]
     3: of the greatest importance; "the all-important subject of
        disarmament"; "crucial information"; "in chess cool nerves
        are of the essence" [syn: {all-important(a)}, {all
        important(p)}, {crucial}, {of the essence(p)}]
     4: being or relating to or containing the essence of a plant
        etc; "essential oil"
     5: applying to essential legal principles and rules of right;
        "substantive law" [syn: {substantive}] [ant: {adjective}]
     6: absolutely required and not to be used up or sacrificed