Notices by Yoïn van Spijk (yvanspijk@toot.community), page 2

Sometimes a spelling mistake becomes standard.

It happened with 'could', the past simple form of 'can'.

'Could' didn't use to have an L. The letter was copied from 'should' and 'would'.

Here you can read why this happened:

The English words 'sad' is etymologically related to German 'satt' (full; done; fed up) and Dutch 'zat' (drunk; fed up; plenty).

Their original Germanic meanings were "full; sated".

These words are also related to Latin 'satis' (enough) and its derivations 'to satisfy' and French 'assez' (enough; quite).

Here's more: