Wordnet 3.0
NOUN (1)
1. 
 a vehicle with a single wheel that is driven by pedals; 
[syn: unicycle, monocycle]
VERB (1)
1.  ride a unicycle; 
WordNet (r) 3.0 (2006):
unicycle
    n 1: a vehicle with a single wheel that is driven by pedals
         [syn: unicycle, monocycle]
    v 1: ride a unicycle