Cycle

A cycle was a unit of time used by several species, including the Sontarans, (COMIC: Pureblood) Chelonians, (PROSE: Zamper) Cybermen, (AUDIO: Hour of the Cybermen) and the Sensorites. (AUDIO: Sphere of Influence)

For Thals, "fifty cycles" was many decades, spanning four generations. (AUDIO: Return to Skaro)