do porridge Definition

porridge
noun

1. A dish of oatmeal or some other cereal which is boiled in water or milk until it reaches a thick consistency. N Amer equivalent oatmeal.
(Brit)
2. slang
A jail sentence.

Idiom: do porridge

(rit)
slang
To serve a prison sentence.
Example: He's doing porridge now

Etymology: 17c in sense 1; 16c in obsolete sense ‘thick soup'; a variant of pottage.