es·sen·tial /ɪˈsɛn(t)ʃəl/
 (a.)必要的,必不可少的;本質的,基本的要素,要點
 es·sen·tial /ɪˈsɛnʧəl/ 形容詞
 本質的,基本的,原發的,必需的,必要的,自發的,特發的,基本的,本質的
 essential
 *本質 基本的
 Es·sen·tial a.
 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 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.”
 5. Mus. Necessary; indispensable; -- said of those tones which constitute a chord, in distinction from ornamental or passing tones.
 6. Med. Idiopathic; independent of other diseases.
 Essential character Biol., the prominent characteristics which serve to distinguish one genus, species, etc., from another.
 Essential disease, Essential fever Med., one that is not dependent on another.
 Essential oils Chem., a class of volatile oils, extracted from plants, fruits, or flowers, having each its characteristic odor, and hot burning taste. They are used in essences, perfumery, etc., and include many varieties of compounds; as lemon oil is a terpene, oil of bitter almonds an aldehyde, oil of wintergreen an ethereal salt, etc.; -- called also volatile oils in distinction from the fixed or nonvolatile.
 Es·sen·tial n.
 1. Existence; being. [Obs.]
 2. That which is essential; first or constituent principle; as, the essentials of religion.
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 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
      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]