noun. Something that bisects, especially a ray that bisects an angle.

noun. A line drawn through the vertex of a triangle so as to bisect either the opposite side (bisector of the side) or the angle (bisector of the angle, or internal bisector), or to bisect the external angle formed by the adjacent sides (external bisector).

noun. One who, or that which, bisects; esp. (Geom.) a straight line which bisects an angle.

noun. A line or curve that bisects or divides a line segment, angle, or other figure into two equal parts.

"You point the hour hand at the sun, and the bisector of the angle between that and 12:00 on the watch is south in the northern hemisphere, north in the southern hemisphere."

angle bisector  perpendicular bisector  

coercivity  dipoles  do  gnomon  headland