circadian
adj biology specialized uk/sɜːˈkeɪ.di.ən/ us/sɝːˈkeɪ.di.ən/
（动植物的）昼夜的，约一日的，约24小时的（节律，周期）
used to describe the processes in animals and plants that happen naturally during a 24-hour period
Our circadian clock makes it difficult to sleep during the day. 昼夜生理时钟让我们很难在白天睡觉。