Witches? Computer coding? Mediaeval music? Geometry?
The cultured thing would be to claim that mediaeval music springs immediately to mind.
But I'm afraid that in my case it's witches.
painting by Hans Baldung
Word To Use Today: hex. The word meaning to cast a spell comes, via Pennsylvanian Dutch, from the German Hexe, witch, and might be linked to the Old High German hagzissa, which is where the English word hag originated.
The computer coding word is short for hexadecimal notation. Hexadecimal means to do with the number sixteen, and hexadecimal notation is necessary when doing arithmetic based on the number sixteen (you use the numbers 1 - 9, and then A - F to represent the numbers from ten to fifteen. It's a bit of a faff for people, but computers find it easier than our usual decimal system).
Hex in mediaeval music is to do with tunes written with the notes of a six-note scale (or based on that idea, anyway).
This idea got renewed attention in the 20th century, when people wanted to find ways of making music without the slightest sign of any tune at all.
In geometry, hex usually stands for hexagon:
honeycombe, photo by Waugsberg
All the to-do-with-six meanings are based on the Greek hex, which means six.