in·dis·pens·able /ˌɪndɪˈspɛn(t)səbəl/
 不可缺少之物(a.)不可缺少的,不能避免的,絕對必要的
 In·dis·pen·sa·ble a.
 1. Not dispensable; impossible to be omitted, remitted, or spared; absolutely necessary or requisite.
 2. Eccl. Not admitting dispensation; not subject to release or exemption. [R.]
    The law was moral and indispensable.   --Bp. Burnet.
 3. Unavoidable; inevitable. [Obs.]
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 indispensable
      adj 1: not to be dispensed with; essential; "foods indispensable to
             good nutrition" [ant: dispensable]
      2: absolutely necessary; vitally necessary; "essential tools
         and materials"; "funds essential to the completion of the
         project"; "an indispensable worker" [syn: essential]
      3: unavoidable; "the routine but indispensable ceremonies of
         state"