quid·di·ty /ˈkwɪdəti/
  本質,實質,詭辯,怪癖,遯辭
  Quid·di·ty n.; pl. Quiddities
  1. The essence, nature, or distinctive peculiarity, of a thing; that which answers the question, Quid est? or, What is it? “ The degree of nullity and quiddity.”
     The quiddity or characteristic difference of poetry as distinguished from prose.   --De Quincey.
  2. A trifling nicety; a cavil; a quibble.
     We laugh at the quiddities of those writers now.   --Coleridge.
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  quiddity
       n 1: an evasion of the point of an argument by raising irrelevant
            distinctions or objections [syn: quibble, cavil]
       2: the essence that makes something the kind of thing it is and
          makes it different from any other [syn: haecceity]