Vertex

vertex
1. (Science: anatomy) A turning point; the principal or highest point; top; summit; crown; apex. Specifically: the top, or crown, of the head.
2. (Science: astronomy) The zenith, or the point of the heavens directly overhead.
3. (Science: mathematics) The point in any figure opposite to, and farthest from, the base; the terminating point of some particular line or lines in a figure or a curve; the top, or the point opposite the base. Vertex of a curve, the point in which the axis pierces the surface.
The principal vertex of a conic section is, in the parabola, the vertex of the axis of the curve: in the ellipse, either extremity of either axis, but usually the left-hand vertex of the transverse axis; in the hyperbola, either vertex, but usually the right-hand vertex of the transverse axis.
Origin: L. Vertex, -icis, a whirl, top of the head, top, summit, from vertere to turn. See Verse, and cf. Vortex.