WordNet sense 1 (an interval during which a recurring sequence of events occurs):

rhythm, round

WordNet sense 2 (the unit of frequency; one hertz has a periodic interval of one second):

hertz, cps, cycles/second, Hz, cycle per second

WordNet sense 3 (a single complete execution of a periodically repeated phenomenon):

oscillation

WordNet sense 4 (a wheeled vehicle that has two wheels and is moved by foot pedals):

bicycle, bike, wheel

WordNet sense 5 (ride a motorcycle):

motorbike, motorcycle

WordNet sense 6 (ride a bicycle):

pedal, pedal