1.  silliness(n = noun.attribute) absurdity, fatuity, fatuousness - a ludicrous folly; "the crowd laughed at the absurdity of the clown's behavior"
is a kind of folly, foolishness, unwiseness
Derived forms adjective silly₃, adjective silly₁

2.  silliness(n = noun.attribute) giddiness - an impulsive scatterbrained manner;
is a kind of frivolity, frivolousness
has particulars: lightness, lightsomeness
Derived form adjective silly₂

   The quality or state of being silly. [1913 Webster]

N  imbecility folly, want of intelligence &c, want of intellect, shadowness, silliness, foolishness, imbecility, incapacity, vacancy of mind, poverty of intellect, weakness of intellect, clouded perception, poor head, apartments to let, stupidity, stolidity, hebetude, dull understanding, meanest capacity, shortsightedness, incompetence, one's weak side, not one's strong point, bias, infatuation, simplicity, puerility, babyhood, dotage, anility, second childishness, fatuity, idiocy, idiotism, driveling, folly, frivolity, irrationality, trifling, ineptitude, nugacity, inconsistency, lip wisdom, conceit, sophistry, giddiness, eccentricity, extravagance, rashness, act of folly, unintelligent, unintellectual, unreasoning, mindless, witless, reasoningless, brainless, halfbaked, having no head, not bright, inapprehensible, weak headed, addle headed, puzzle headed, blunder headed, muddle headed, muddy headed, pig headed, beetle headed, buffle headed, chuckle headed, mutton headed, maggoty headed, grossheaded, beef headed, fat witted, fat-headed, weak-minded, feeble-minded, dull minded, shallow minded, lack- brained, rattle-brained, rattle headed, half witted, lean witted, short witted, dull witted, blunt-witted, shallow-pated, clod-pated, addle- pated, addle-brained, dim-sighted, short-sighted, thick-skulled, weak in the upper story, shallow, borne, weak, wanting, soft, sappy, spoony, dull, dull as a beetle, stupid, heavy, insulse, obtuse, blunt, stolid, doltish, asinine, inapt, prosaic, hebetudinous, childish, child-like, infantine, infantile, babyish, babish, puerile, anile, simple, old-womanish, fatuous, idiotic, imbecile, driveling, blatant, babbling, vacant, sottish, bewildered, blockish, unteachable Boeotian, Boeotic, bovine, ungifted, undiscerning, unenlightened, unwise, unphilosophical, apish, simious, foolish, silly, senseless, irrational, insensate, nonsensical, inept, maudlin, narrow-minded, bigoted, giddy, rash, eccentric, foolish, unwise, injudicious, improper, unreasonable, without reason, ridiculous, absurd, idiotic, silly, stupid, asinine, ill-imagined, ill-advised, ill-judged, ill-devised, mal entendu, inconsistent, irrational, unphilosophical, extravagant, sleeveless, idle, pointless, useless, inexpedient, frivolous, Davus sum non, a fool's bolt is soon shot clitellae bovi sunt im, fools rush in where angels fear to tread, il n' a ni bouche ni eperon, the bookful blockhead, ignorantly read, to varnish nonsense with the charms of sound.