1.  nonentity(n = noun.state) nonexistence - the state of not existing;
is a kind of nonbeing
has particulars: irreality, unreality, nihility, nothingness, nullity, void, impossibility, impossibleness

2.  nonentity(n = noun.person) cipher, cypher, nobody - a person of no influence;
is a kind of common man, common person, commoner
has particulars: pip-squeak, small fry, squirt, jackanapes, lightweight, whippersnapper

1.  Nonexistence; the negation of being. [1913 Webster]

2.  A thing not existing. South. [1913 Webster]

3.  A person or thing of little or no account; an unimportant person; -- usually used as a disparaging term. [1913 Webster]

nonentity, n. (pl. -ies)
1 a person or thing of no importance.
2 a non-existence. b a non-existent thing, a figment.

Etymology:
med.L nonentitas non-existence

N  inexistence, nonexistence, nonsubsistence, nonentity, nil, negativeness, nullity, nihility, nihilism, tabula rasa, blank, abeyance, absence, no such thing, nonbeing, nothingness, oblivion, annihilation, extinction, extinguishment, extirpation, Nirvana, obliteration, inexistent, nonexistent, negative, blank, missing, omitted, absent, insubstantial, shadowy, spectral, visionary, unreal, potential, virtual, baseless, in nubibus, unsubstantial, vain, unborn, uncreated, unbegotten, unconceived, unproduced, unmade, perished, annihilated extinct, exhausted, gone, lost, vanished, departed, gone with the wind, defunct, fabulous, ideal, supposititious &c, negatively, virtually, non ens.

N  unsubstantiality, insubstantiality, nothingness, nihility, no degree, no part, no quantity, no thing, nothing, naught, nil, nullity, zero, cipher, no one, nobody, never a one, ne'er a one, no such thing, none in the world, nothing whatever, nothing at all, nothing on earth, not a particle, all talk, moonshine, stuff and nonsense, matter of no importance, matter of no consequence, thing of naught, man of straw, John Doe and Richard Roe, faggot voter, nominis umbra, nonentity, flash in the pan, vox et praeterea nihil, shadow, phantom, dream, ignis fatuus, such stuff as dreams are made of, air, thin air, vapor, bubble, baseless fabric of a vision, mockery, hollowness, blank, void, inanity, fool's paradise, unsubstantial, baseless, groundless, ungrounded, without foundation, having no foundation, visionary, immaterial, spectral, dreamy, shadowy, ethereal, airy, cloud built, cloud formed, gossamery, illusory, insubstantial, unreal, vacant, vacuous, empty, eviscerated, blank, hollow, nominal, null, inane, there's nothing in it, an ocean of dreams without a sound.

N  unimportance, insignificance, nothingness, immateriality, triviality, levity, frivolity, paltriness, poverty, smallness, vanity, matter of indifference, no object, nothing, nothing to signify, nothing worth speaking of, nothing particular, nothing to boast of, nothing to speak of, small matter, no great matter, trifling matter, mere joke, mere nothing, hardly anything, scarcely anything, nonentity, small beer, cipher, no great shakes, peu de chose, child's play, kinderspiel, toy, plaything, popgun, paper pellet, gimcrack, gewgaw, bauble, trinket, bagatelle, Rickshaw, knickknack, whim-wham, trifle, trifles light as air, yankee notions, trumpery, trash, rubbish, stuff, fatras, frippery, leather or prunello, chaff, drug, froth bubble smoke, cobweb, weed, refuse, scum, joke, jest, snap of the fingers, fudge, fiddlestick, fiddlestick end, pack of nonsense, mere farce, straw, pin, fig, button, rush, bulrush, feather, halfpenny, farthing, brass farthing, doit, peppercorn, jot, rap, pinch of snuff, old son, cent, mill, picayune, pistareen, red cent, minutiae, details, minor details, small fry, dust in the balance, feather in the scale, drop in the ocean, flea-bite, molehill, nine days' wonder, ridiculus mus, flash in the pan, much ado about nothing, unimportant, of little account, of small account, of no account, of little importance, of no importance, immaterial, unessential, nonessential, indifferent, subordinate, mediocre, passable, fair, respectable, tolerable, commonplace, uneventful, mere, common, ordinary, inconsiderable, so-so, insignificant, inappreciable, trifling, trivial, slight, slender, light, flimsy, frothy, idle, puerile, airy, shallow, weak, powerless, frivolous, petty, niggling, piddling, peddling, fribble, inane, ridiculous, farcical, finical, finikin, fiddle-faddle, fingle-fangle, namby-pamby, wishy-washy, milk and water, poor, paltry, pitiful, contemptible, sorry, mean, meager, shabby, miserable, wretched, vile, scrubby, scrannel, weedy, niggardly, scurvy, putid, beggarly, worthless, twopennyhalfpenny, cheap, trashy, catchpenny, gimcrack, trumpery, one- horse, not worth the pains, not worth while, not worth mentioning, not worth speaking of, not worth a thought, not worth a curse, not worth a straw, beneath notice, unworthy of notice, beneath regard, unworthy of regard, beneath consideration, unworthy of consideration, de lana caprina, vain, slightly, rather, somewhat, pretty well, tolerably, for aught one cares, Int, no matter!, pish!, tush!, tut!, pshaw!, pugh!, pooh, pooh-pooh!, fudge!, bosh!, humbug!, fiddlestick, fiddlestick end!, fiddlededee!, never mind!, n'importe!, what signifies it, what boots it, what of it, what of that, what matter, what's the odds, a fig for', stuff!, nonsense!, stuff and nonsense, magno conatu magnas nugas, le jeu ne vaut pas la chandelle, it matters not, it does not signify, it is of no consequence, it is of no importance, elephantus non capit murem, tempete dans un verre d'eau.