Source : Webster's Revised Unabridged Dictionary (1913)

Tricycle \Tri"cy*cle\, n. [Pref. tri- + cycle as inbicycle.]
   A three-wheeled velocipede. See Illust. under {Velocipede}.
   Cf. {Bicycle}.

Source : WordNet®

tricycle
     n : a vehicle with three wheels that is moved by foot pedals
         [syn: {trike}, {velocipede}]