Why did 's' in 'wisard' change to 'z'

Wizard:

  1. a man in stories who has magic powers
  2. someone who is very good at something

Origin and usage: The word wizard comes from the Middle English word 'wys' meaning 'wise'. In this sense, it first appeared in English in the early 15th century. As a word used to describe a man with magical powers, wizard did not start to be used until around 1550 - MacMillan Blog

The word wizard is derived from wise.

Wizard -> wise + ard

Wikitionary says wisard is archaic form of wizard.


Wize: Obsolete form of 'wise' — Wiktionary


The 's' in wisard changed to 'z' and 'z' in wize changed to 's'.

Questions:

  • Why did the 's' in 'wisard' change to 'z'?
  • Why did the 'z' in 'wize' change to 's'?

A smart* person might have cogni(z|s)ance of another word where the original s changed to a z. According to the OED, this change (in the spelling of cognisance) was due to the fact that the s sounds like a z. But a spelling with the original s also survives.

There are many such words, usually where the z spelling is used in the US and s is used in the UK. In some cases, like seize/seise plus their adjective forms seizable/seisable, the original s spelling is only used in a niche meaning.

I think therefore that wizard switched to a z because that’s what it sounds like. And other words like wise did not because they just kept their old spelling.

* Or someone who knows how to search in the right places :p