lunar month
Astronomical term for the period of one complete cycle of the moon's phases, approximately 29.5 days.
太陰月は約29.5日です。
A lunar month is about 29.5 days.
Synonym also meaning lunar month; 太陰月 is slightly more common in general contexts.
Solar month, based on the sun's position; contrasts with the moon-based 太陰月.
From 太陰 (たいいん, 'moon', literally 'great yin') + 月 (げつ, 'month'). The term 太陰 is a classical Chinese-derived word for the moon, contrasting with 太陽 (たいよう, 'sun').