Emily Dickinson Lexicon

VERT'EX, n. [L. from verto, to turn; primarily a round point.]

1. The crown or top of the head. – Coxe.
2. The top of a hill or other thing; the point of a cone, pyramid, angle or figure; the pole of a glass, in optics. The vertex of a curve, is the point from which the diameter drawn, or the intersection of the diameter and the curve.
3. In astronomy, the zenith; the point of the heavens perpendicularly over the head. – Cyc.