vertex

Vertex, verticis, m., third declension, from verto, "turn", and the sense history follows the turning. First the thing that visibly spins: a whirlpool, an eddy of wind or flame. Then the crown of the head, where the hair grows in a spiral. Then, by ordinary extension upwards, any summit or peak.

Vortex is the same word with the older o-vowel preserved; Latin used both spellings for both meanings, and it is English that split them into two separate words with two separate jobs. The English geometric vertex and the adjective vertical both descend from the top-of-the-head sense, not from the whirlpool one.