TIL that prior to the adoption of the internationally accepted A4 std sheet, Britain's standard paper size was called "foolscap".

Its unique name is because the paper was watermarked with the symbol of a joker with a fool's cap and bells. It's slightly bigger than an A4 sheet

If one digs back to the etymology a bit more, John Ciardi says that the watermark “foolscap” was actually a mistranslation of an earlier reference to legal paper.

In the middle ages, contracts were drawn upon a large sheet of paper, & both parties signed. (1/)

The paper was then torn in 2 (in a ragged fashion) & 1 half was given to each party. The ragged tear was unique to that particular contract. If there was any dispute the parties would each bring their 1/2 before a judge who would 1st check if the 2 halves lined up perfectly. 2/

If they did, then he knew he was looking at the real contract. If not, then he knew one party at least had altered their half. (3/)

The paper was referred to as “folio capa” which over the years was shortened in speech to folioscapa and then transliterated to foolscap. Of course, the watermark came late in this process, and was a symbol of a fool’s cap. (4/)

Credit: Micheal Miller, https://tinyurl.com/y2oyq6xl 

The funny thing is while its been centuries since the days of "foolscap" paper we are still relying on antiquated methods of checking the authenticity of legal documents.

Just ask anyone who has had to sign 100s of pages of contracts during an M&A.

Thankfully, there are people solving for this (which is the bane of every A0 lawyer):

(1) Leegality, https://leegality.com/ , which is taking the "paper" out of paperwork (caveat: fren works here);
(2) SignEasy, https://signeasy.com/ 

Do feel free to include other names below