The Collaborative International Dictionary of English v.0.48:

Tomfoolery \Tom`fool"er*y\, n.
   Trifling or silly behavior done mostly for amusement;
   foolishness; fooling around.

   Syn: tomfoolishness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

tomfoolery
    n 1: foolish or senseless behavior [syn: folly, foolery,
         tomfoolery, craziness, lunacy, indulgence]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "tomfoolery":
   antic, balderdash, baloney, banter, blatherskite, buffoonery,
   caper, claptrap, clownishness, foolery, fooling, frolic,
   harlequinade, hogwash, horseplay, lark, malarkey, monkeyshine,
   monkeyshines, poppycock, rubbish, shenanigan, shenanigans, shines,
   trick, twaddle