What is another word for circadian?
Pronunciation: [sɜːkˈe͡ɪdi͡ən] (IPA) 
Circadian, the term used to describe an organism's natural 24-hour cycle, has a variety of synonyms. One commonly used alternative is diurnal, which specifically references the day portion of this cycle. Other options include nycthemeral, referring to both day and night, and ultradian, which describes cycles shorter than 24 hours. Chronobiological and bioperiodic are more scientific alternatives, while biorhythmic and biological clock are more colloquial. Finally, there are several related terms, such as nocturnal (active during the night), crepuscular (active at dawn and dusk), and matutinal (active in the morning), which all relate to different parts of the circadian cycle.
