oatmeal

From Middle English otemele, a combination of ote ("oat") and mele ("meal, coarse-ground grains"). It's directly equivalent to modern "oat" + "meal."

The word has stayed remarkably transparent — it's meant coarsely ground oats since Middle English, with the compound simply carrying forward unchanged into today's spelling.

It shares its second half with other "meal" words describing ground grains, since "mele" in Middle English meant coarse-ground grain generally, not just oats.