Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

wacky
     adj 1: pungent adjectives of disesteem; "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},
            {whacky}, {zany}, {unreasonable}]
     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}, {whacky}]
     [also: {wackiest}, {wackier}]