[1] : The Collaborative International Dictionary of English v.0.48

nonexistence \non`exist"ence\, n.
   1. the state of not existing; absence of existence; the
      negation of being; -- usually used with reference to
      existince in the real world, or logical possiblity; as,
      the nonexistence of vaporware does not go unnoticed long.
      --a. baxter.

   syn: nonentity1.
        1913 webster +pjc

   2. a thing that has no existence. --sir t. browne.
      1913 webster

[2] : WordNet (r) 2.0

nonexistence
     n : the state of not existing syn: nonentity ant: being
see also:
nonentity being 

Nonexistence >> N Words
Nonexistence, definition of term: Nonexistence
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