The infallible mental clock that had been set ticking during the Spice Agony told her she had adapted to the planet's circadian rhythms.
Frank Herbert
Chapterhouse: Dune
sɜrˈkeɪ.di.ən
adjective
relating to or recurring at approximately 24-hour intervals
The term 'circadian' is derived from the Latin words 'circa' (which means 'around') and 'diem' (which means 'day'). Circadian rhythms are natural processes that follow a daily cycle, such as the sleep-wake cycle in humans.
The infallible mental clock that had been set ticking during the Spice Agony told her she had adapted to the planet's circadian rhythms.
Frank Herbert
Chapterhouse: Dune