vertex

Concise Oxford English Dictionary © 2008 Oxford University Press:
vertex /ˈvəːtɛks/

▶noun (pl. vertices /-tɪsiːz/ or vertexes)

• 1 the highest point; the top or apex.

• 2 Geometry each angular point of a polygon, polyhedron, or other figure.

  ■ a meeting point of two lines that form an angle.

• 3 Anatomy the crown of the head.

– origin ME: from L., ‘whirlpool, crown of a head, vertex’, from vertere ‘to turn’.