Source : Webster's Revised Unabridged Dictionary (1913)

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.

            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.

Source : WordNet®

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}]