[JacobAldridge]

I always remember c as the constant speed of light [in a vacuum], but never pondered the actual origin beyond the perhaps rudimentary algebra “x, y, z are variables and a, b, c are constants”.

I don’t think I thought c came from “constant”, because that’s a very English-centric view of science, but the annoying thing about reading a smart article like this is that it’s impossible to explore the depths of how your mind worked before acquiring the knowledge!

[Rygian]

As a tongue in cheek remark, it is English-centric to think that using c for constants is an English-centric view of science. French, Spanish, Italian, Portuguese, Romanian, all use the same word of Latin origin.

[guerrilla]

I think it would have been 'k' if it stood for "constant" since most of them were German-speakers or collaborating with them.

[UncleSlacky]

k was already in use as Boltzmann's constant by that time, I think:

https://en.wikipedia.org/wiki/Boltzmann_constant