The Collaborative International Dictionary of English v.0.48:

Fad \Fad\ (f[a^]d), n. [Cf. Faddle.]
   1. A hobby; freak; whim.
      [1913 Webster]

            It is your favorite fad to draw plans. --G. Eliot.
      [1913 Webster]

   2. a practise followed enthusiastically by a number of people
      for a limited period of time; as, the latest fad in
      fashion.

   Syn: craze; mania.
        [PJC] -- Fad"dist, n.
        -- Fad"dish, a.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

faddish \faddish\ faddy \faddy\adj.
   1. intensely fashionable for a short time. [WordNet sense 1]

   Syn: trendy. [WordNet 1.5]

   2. prone to follow fads; as, a faddish clique of teenagers;
      -- of people.

   Syn: trendy. [PJC]

WordNet (r) 3.0 (2006):

faddish
    adj 1: intensely fashionable for a short time [syn: faddish,
           faddy]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "faddish":
   changeable, coquettish, faddy, fickle, flighty, flirtatious,
   inconstant, light, mercurial, quicksilver, skittish, toying,
   undependable, unpredictable, unreliable, vacillating, versatile,
   volatile