sector
We always referred to that as an arc.
It is a sector
A sector.
an O another name for a circle is an O and a spherical
another name for a half circle is semi-circle
square circle
There really isn't one, but I suspect the phrase you're looking for is "sector of a circle."
Another name for half a circle is a semicircle.
A circle.
A pie chart, a cake slice chart.
Another name for malaria that starts with an A and has 4 letters is ague.
circumference