The Collaborative International Dictionary of English v.0.48:

Fatuity \Fa*tu"i*ty\, n. [L. fatuitas, fr. fatuus foolish: cf.
   F. fatuit['e] Cf. Fatuous.]
   Weakness or imbecility of mind; stupidity.
   [1913 Webster]

         Those many forms of popular fatuity.     --I Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fatuity
    n 1: a ludicrous folly; "the crowd laughed at the absurdity of
         the clown's behavior" [syn: absurdity, fatuity,
         fatuousness, silliness]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "fatuity":
   absurdity, aimlessness, asininity, battiness, blank mind,
   blankmindedness, blankness, bootlessness, brainlessness,
   buffoonery, calm of mind, clownishness, counterproductiveness,
   counterproductivity, crackpottedness, crankiness, craziness,
   daffiness, desipience, eccentricity, emptiness, emptiness of mind,
   empty-headedness, failure, fallow mind, fatuousness, fecklessness,
   folly, foolery, foolheadedness, foolishness, frivolity,
   frivolousness, fruitlessness, futility, giddiness, goofiness,
   hollowness, idiocy, imbecility, impotence, inanity,
   ineffectiveness, ineffectuality, ineffectualness,
   inefficaciousness, inefficacy, ineptitude, insanity, invalidity,
   lunacy, madness, meaninglessness, mental blankness, mindlessness,
   niaiserie, nirvana, nugacity, nuttiness, oblivion, otiosity,
   passivity, pointlessness, profitlessness, purposelessness,
   queerness, quietism, rat race, sappiness, screwiness,
   senselessness, silliness, stupidity, tabula rasa, the absurd,
   thoughtfreeness, thoughtlessness, tranquillity, triflingness,
   triviality, unintelligence, unproductiveness, unprofitability,
   unprofitableness, uselessness, vacancy, vacuity, valuelessness,
   vanity, vicious circle, wackiness, weirdness, witlessness,
   worthlessness, zaniness, zanyism