The Collaborative International Dictionary of English v.0.48:

zany \za"ny\ (z[=a]"n[-e]), adj.
   Comical in a clownish or buffoonish manner; whimsically
   comical.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Zany \Za"ny\, n.; pl. Zanies. [It. zanni a buffoon,
   merry-andrew, orig. same as Giovanni John, i. e., merry John,
   L. Ioannes, Gr. ?, Heb. Y[=o]kh[=a]n[=a]n, prop., the Lord
   graciously gave: cf. F. zani, fr. the Italian. Cf.
   Jenneting.]
   A merry-andrew; a buffoon.
   [1913 Webster]

         Then write that I may follow, and so be
         Thy echo, thy debtor, thy foil, thy zany. --Donne.
   [1913 Webster]

         Preacher at once, and zany of thy age.   --Pope.
   [1913 Webster]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Zany \Za"ny\, v. t.
   To mimic. [Obs.]
   [1913 Webster]

         Your part is acted; give me leave at distance
         To zany it.                              --Massinger.
   [1913 Webster]

WordNet (r) 3.0 (2006):

zany
    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: like a clown; "a buffoonish walk"; "a clownish face"; "a zany
       sense of humor" [syn: buffoonish, clownish, clownlike,
       zany]
    n 1: a buffoon in one of the old comedies; imitates others for
         ludicrous effect
    2: a man who is a stupid incompetent fool [syn: fathead,
       goof, goofball, bozo, jackass, goose, cuckoo,
       twat, zany]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "zany":
   Columbine, Hanswurst, Harlequin, Pantalone, Pantaloon,
   Polichinelle, Pulcinella, Punch, Punchinello, Scaramouch, absurd,
   ament, amusing, ass, banana, born fool, buffo, buffoon, burlesquer,
   card, caricaturist, clown, clownish, comedian, comic, comical,
   crackpot, crazy, cretin, cutup, doodle, egregious ass,
   epigrammatist, exhibitionist, farceur, figure of fun, fool,
   foolish, frolicsome, funny, funnyman, gag writer, gagman, gagster,
   gay, goofy, half-wit, harlequin, hilarious, humorist, idiot,
   ignoramus, imbecile, inane, ironist, jack-pudding, jackass, jester,
   joker, jokesmith, jokester, kooky, lampooner, loony, ludicrous,
   lunatic, mad, madcap, merry, merry-andrew, milksop, mooncalf,
   moron, motley, motley fool, natural, nonsensical, nut, nutty,
   parodist, perfect fool, pickle-herring, playful, practical joker,
   prankster, punner, punster, quipster, reparteeist, satirist,
   schmuck, screwball, show-off, silly, simpleton, slapstick,
   softhead, sop, sportive, stupid ass, tomfool, trickster, wacky,
   wag, wagwit, wild, wisecracker, wit, witling



The Devil's Dictionary (1881-1906):

ZANY, n.  A popular character in old Italian plays, who imitated with
ludicrous incompetence the _buffone_, or clown, and was therefore the
ape of an ape; for the clown himself imitated the serious characters
of the play.  The zany was progenitor to the specialist in humor, as
we to-day have the unhappiness to know him.  In the zany we see an
example of creation; in the humorist, of transmission.  Another
excellent specimen of the modern zany is the curate, who apes the
rector, who apes the bishop, who apes the archbishop, who apes the
devil.