Heavens! And what of the etymology of this very strange-looking word?

"Etymology: sizar alteration of sizer, from 1size
Date: 1588"

MW

Now that 1size, according to my online search, comes from assize, which makes no sense at all:

"1 a : a judicial inquest b : an action to be decided by such an inquest, the writ for instituting it, or the verdict or finding rendered by the jury"