ne·ces·si·ty /nɪˈsɛsəti, ˈsɛsti/
 必須,需要,必然,必需品
 Ne·ces·si·ty n.; pl. Necessities
 1. The quality or state of being necessary, unavoidable, or absolutely requisite; inevitableness; indispensableness.
 2. The condition of being needy or necessitous; pressing need; indigence; want.
    Urge the necessity and state of times.   --Shak.
    The extreme poverty and necessity his majesty was in.   --Clarendon.
 3. That which is necessary; a necessary; a requisite; something indispensable; -- often in the plural.
 These should be hours for necessities,
 Not for delights.   --Shak.
 What was once to me
 Mere matter of the fancy, now has grown
 The vast necessity of heart and life.   --Tennyson.
 4. That which makes an act or an event unavoidable; irresistible force; overruling power; compulsion, physical or moral; fate; fatality.
 So spake the fiend, and with necessity,
 The tyrant's plea, excused his devilish deeds.   --Milton.
 5. Metaph. The negation of freedom in voluntary action; the subjection of all phenomena, whether material or spiritual, to inevitable causation; necessitarianism.
 Of necessity, by necessary consequence; by compulsion, or irresistible power; perforce.
 Syn: -- See Need.
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 necessity
      n 1: the condition of being essential or indispensable
      2: 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: essential, requirement, requisite, necessary]
         [ant: inessential]