Pronunciation: (i-kwā'tur),[key] —n. 1. the great circle on a sphere or heavenly body whose plane is perpendicular to the axis, equidistant everywhere from the two poles of the sphere or heavenly body.
2. the great circle of the earth that is equidistant from the North Pole and South Pole.
3. a circle separating a surface into two congruent parts.
4. See celestial equator.