also: にちげつ
noun
Refers to the celestial bodies themselves, often in poetic or literary contexts.
日月が空に輝いている。
The sun and moon are shining in the sky.
日月が経つのは早いものだ。
How quickly the days and months pass.
noun
Sunday and Monday
Only with reading にちげつ
Abbreviation used in schedules or contexts where days of the week are listed; reading is restricted to にちげつ.
日月は休みです。
We are closed on Sunday and Monday.
月日 (つきひ) also means 'time' or 'days and months', but is more common in everyday speech. 日月 (じつげつ/にちげつ) is more literary and can specifically refer to the sun and moon.
Compound of 日 (sun, day) and 月 (moon, month). The reading じつげつ uses the on'yomi, while にちげつ mixes on'yomi and kun'yomi. The time-related sense is a natural extension of the celestial bodies marking the passage of time.