You can end up in a wheelchair if you abuse NOx. Severe B12 deficiency will damage the nervous system.

It started with branding. Like CD stands for CompactDisc which was a trademarked brand name using this logo.

Edit: I’m wrong. There is a patent for an optical disc that precedes CD and Laserdisc and uses the word Disc on the patent

That’s probably where disc started being used for optical storage. And disk remained being used for magnetic storage.