noun
new moon; first day of the lunar month
Refers to the astronomical new moon when the moon is not visible, or the first day of the lunar calendar month.
今夜は新月で、月がまったく見えない。
Tonight is the new moon, so the moon is completely invisible.
旧暦では新月の日が月の始まりだった。
In the old lunar calendar, the day of the new moon was the start of the month.
noun
Sometimes used loosely for a thin crescent moon, though 三日月 is the more precise term. This usage is less common and may be considered non-standard.
See also: 三日月
空に細い新月が浮かんでいた。
A thin crescent moon hung in the sky.