From 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]