This article mentions the “schert”:
https://www.thoughtco.com/medieval-underwear-1788621
At first I thought this meant and was pronounced like “skirt”. But on reading this, I think maybe it means and is pronounced like “shirt”:
“Over their hose and any underpants they might wear, both men and women usually wore a schert, chemise, or undertunic.”
I wasn’t able to figure this out using Google. Is anyone familiar with this term, what it means in this context, and how it’s pronounced?
It's pronounced 'shirt,' essentially, and is, like the article describes, an undergarment that goes between the wearer's skin and tunic, to help keep the tunic clean and sweat-free.