The Collaborative International Dictionary of English v.0.48:

Wacke \Wack"e\, Wacky \Wack"y\, n. [G. wacke, MHG. wacke a large
   stone, OHG. waggo a pebble.] (Geol.)
   A soft, earthy, dark-colored rock or clay derived from the
   alteration of basalt.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wacky
    adj 1: ludicrous, foolish; "gave me a cockamamie reason for not
           going"; "wore a goofy hat"; "a silly idea"; "some wacky
           plan for selling more books" [syn: cockamamie,
           cockamamy, goofy, sappy, silly, wacky,
           whacky, zany]
    2: informal or slang terms for mentally irregular; "it used to
       drive my husband balmy" [syn: balmy, barmy, bats,
       batty, bonkers, buggy, cracked, crackers, daft,
       dotty, fruity, haywire, kooky, kookie, loco,
       loony, loopy, nuts, nutty, round the bend, around
       the bend, wacky, whacky]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "wacky":
   abnormal, absurd, anomalous, apish, asinine, balmy, bananas, barmy,
   bats, batty, beany, befooled, beguiled, besotted, bonkers,
   brainless, buffoonish, buggy, bughouse, bugs, cockeyed, cracked,
   crackers, crank, crankish, cranky, crazed, crazy, credulous,
   crotchety, cuckoo, daffy, daft, dazed, demented, deranged, deviant,
   deviative, different, dippy, divergent, dizzy, doting, dotty, dumb,
   eccentric, erratic, exceptional, fatuitous, fatuous, fey, flaky,
   flipped, fond, fool, foolheaded, foolish, freaked-out, freakish,
   fruitcakey, fruity, fuddled, funny, futile, gaga, goofy, gulled,
   harebrained, haywire, idiocratic, idiosyncratic, idiotic, imbecile,
   inane, inept, infatuated, insane, irregular, just plain nuts,
   kinky, kooky, loony, loopy, lunatic, mad, maggoty, maudlin,
   moronic, nuts, nutty, odd, oddball, off the hinges, off the track,
   off the wall, peculiar, potty, preposterous, queer, quirky,
   round the bend, sappy, screwball, screwballs, screwy, senseless,
   sentimental, silly, singular, slaphappy, strange, stupid,
   thoughtless, twisted, unconventional, unnatural, wet, whimsical,
   witless