Translation guide
The English term 'half-moon' can refer to the astronomical phase (first/last quarter), a semicircular shape, or a crescent shape. Japanese distinguishes these carefully, and the most natural translation depends on context.
Referring to the moon phase when exactly half of the visible disk is illuminated, i.e., the first quarter or last quarter moon.
The standard astronomical term for a half-moon (first or last quarter). Can also refer to a semicircular shape in some contexts.
今夜は半月が見える。
You can see a half-moon tonight.
Specifically the first quarter moon (waxing half-moon). Used in astronomical or poetic contexts.
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 (waning half-moon). Used in astronomical or poetic contexts.
下弦の月は明け方に見える。
The last quarter moon can be seen around dawn.
Describing something shaped like a half-circle, such as a half-moon window, table, or design.
Literally 'half-moon shape'. Used for objects, designs, or architectural features that are semicircular.
その窓は半月形をしている。
That window is shaped like a half-moon.
Means 'semicircular shape'. More geometric and less specifically 'moon-like' than 半月形, but often interchangeable.
In casual English, 'half-moon' sometimes refers to a crescent shape. Japanese distinguishes this clearly.
Literally 'third-day moon', meaning a crescent moon. This is the most natural word for a crescent shape, even if English calls it a 'half-moon'.
If you mean a true half-circle (semicircle), use 半月形 or 半円形. 三日月 is specifically a crescent.
三日月形のパンを焼いた。
I baked half-moon shaped bread (crescent rolls).
Crescent-shaped. Used for objects like pastries, jewelry, or designs.
English 'half-moon' can be ambiguous. In Japanese, 半月 (はんげつ) is a half-circle (astronomical quarter moon or semicircle), while 三日月 (みかづき) is a crescent. Using the wrong one can cause confusion.
半月は半円、三日月は細い弧の形です。
半月 is a semicircle, 三日月 is a thin arc shape.
I bought a half-moon table.
She's wearing half-moon earrings.