The Collaborative International Dictionary of English v.0.48:

Porridge \Por"ridge\, n. [Probably corrupted fr. pottage; perh.
   influenced by OE. porree a kind of pottage, OF. porr['e]e,
   fr. L. porrum, porrus, leek. See Pottage, and cf.
   Porringer.]
   A food made by boiling some leguminous or farinaceous
   substance, or the meal of it, in water or in milk, making of
   broth or thin pudding; as, barley porridge, milk porridge,
   bean porridge, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

porridge
    n 1: soft food made by boiling oatmeal or other meal or legumes
         in water or milk until thick