noun, used as a prefix
diurnal; daily cycle
Technical prefix used in scientific or astronomical contexts to describe phenomena related to a 24-hour day, such as 日周運動 (diurnal motion).
日周運動は地球の自転によって起こる。
Diurnal motion is caused by the Earth's rotation.
この生物の日周リズムは光に影響される。
The diurnal rhythm of this organism is influenced by light.
Compound of 日 (sun, day) and 周 (cycle, circumference), literally 'day cycle'. The reading にっしゅう is a regular on'yomi combination.