first or last quarter
A week after the Full Moon the Moon looks like a semi circle again, this phase is called ''Third Quarter''
first or last quarter
Half a circle is called a semicircle
The phase of the moon is called a first quarter or last quarter moon when it appears as a semi-circle. This occurs when the moon is at a 90-degree angle relative to the Earth and the Sun, resulting in half of the illuminated side facing Earth.
a hemisphere
Half a circle is called a "semicircle" in geometry.
Half a circle is called a semi-circle. Sometimes it is called a half-moon.
semicircleA half circle is called a semicircle.Half a circle is a semi-circle
That's the "gibbous" phase.
Semi = half
The half circle American flags are called "half-staff flags."
Half the diameter of a circle is called its radius.