ver·tex 
(vûrtĕks′)
(vûrtĕks′)n. pl. ver·ti·ces (-tĭ-sēz′) also ver·tex·es
1. The highest point; the apex or summit: the vertex of a mountain.
2. Anatomy
a. The highest point of the skull.
b. The top of the head.
3. In astrology, the highest point reached in the apparent motion of a celestial body.
4. Mathematics
a. The point at which the sides of an angle intersect.
b. The point on a triangle or pyramid opposite to and farthest away from its base.
c. A point on a polyhedron common to three or more sides.
d. A point of maximal curvature on a parabola or hyperbola.
[Latin, whirlpool, crown of the head (where the hair forms a whorl), vertex, from vertere, to turn; see wer-2 in the Appendix of Indo-European roots.]