oatmeal vs porridge

oatmeal and porridge both are nouns.

Word	Noun	Adjective	Verb	Adverb
oatmeal	Yes	No	No	No
porridge	Yes	No	No	No

As nouns, porridge is a hypernym of oatmeal; that is, porridge is a word with a broader meaning than oatmeal:

oatmeal: porridge made of rolled oats
porridge: soft food made by boiling oatmeal or other meal or legumes in water or milk until thick

oatmeal (noun)	porridge (noun)
porridge made of rolled oats	soft food made by boiling oatmeal or other meal or legumes in water or milk until thick
meal made from rolled or ground oats