Source : Webster's Revised Unabridged Dictionary (1913)

Nonentity \Non*en"ti*ty\, n.; pl. {Nonentities}.
   1. Nonexistence; the negation of being.

   2. A thing not existing. --South.

   3. A person or thing of little or no account. [Colloq.]

Source : WordNet®

nonentity
     n 1: the state of not existing [syn: {nonexistence}] [ant: {being}]
     2: a person of no influence [syn: {cipher}, {cypher}, {nobody}]
     3: a nonexistent thing [syn: {nothing}]