The Collaborative International Dictionary of English v.0.48:

Quiddity \Quid"di*ty\, n.; pl. Quiddities. [LL. quidditas, fr.
   L. quid what, neut. of quis who, akin to E. who: cf. F.
   quiddit['e].]
   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." --Bacon.
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            The quiddity or characteristic difference of poetry
            as distinguished from prose.          --De Quincey.
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   2. A trifling nicety; a cavil; a quibble.
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            We laugh at the quiddities of those writers now.
                                                  --Coleridge.
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