Decade

A decade was a unit of time equal to ten years. (AUDIO: The Morton Legacy)

The Brynblaidd cannibals had a tradition of butchering travellers once every decade. (TV: Countrycide)

The Doctor spent "decades" during the latter part of his second incarnation on Darron, learning the psychic techniques of the Mind Monks. (PROSE: The Quantum Archangel)