Thin porridge (5)
I believe the answer is:
gruel
'thin porridge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gruel that I've seen before include "cheap fare" , "Thin liquid food" , "Unappetising meal of boiled oatmeal" , "Thin food of boiled oatmeal" , "sloppy fare" .)