noun
half-moon; quarter moon
Astronomical term for the moon at first or last quarter, when it appears as a half circle. Often used in compounds like 上弦の月 (first quarter moon) and 下弦の月 (last quarter moon).
今夜は弦月がきれいに見える。
Tonight the half-moon is clearly visible.
上弦の月は夕方に南の空に見える。
The first quarter moon can be seen in the southern sky in the evening.
Specifically the last quarter moon, a subset of 弦月.
Compound of 弦 (string, bowstring, crescent) and 月 (moon), referring to the moon's shape resembling a bow. The exact historical derivation is uncertain.