An account of siege food during the Boer war described it as "a paste closely akin to that used by bill-stickers...a sour kind of mess, but very healthy and filling".
Here's a recipe description from the early 1800s:
The mealy sid, or hull of the ground oat, is steeped in blood-warm water, for about two days, when it is wrung out, and the liquor put through a search [sieve]; if it is too thick, they add a little fresh cold water to it, and then set it on the fire to boil, constantly stirring it, till it thickens, and continuing the boiling till it becomes tough like a paste. In the stirring they add a little salt, and dish it up for table.
The result was usually served with butter or milk.
Etymology: From Gaelic sùghan, juice or sauce.
(I'm posting my Monday word a day early, as this will be a busy week for me.)