The Collaborative International Dictionary of English v.0.48:

Oatmeal \Oat"meal`\, n.
   1. Meal made of oats. --Gay.
      [1913 Webster]

   2. (Bot.) A plant of the genus Panicum; panic grass.
      [1913 Webster]

WordNet (r) 3.0 (2006):

oatmeal
    n 1: porridge made of rolled oats [syn: oatmeal, burgoo]
    2: meal made from rolled or ground oats [syn: oatmeal, rolled
       oats]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "oatmeal":
   breakfast food, cereal, cornflakes, dry cereal, farina, frumenty,
   grits, gruel, hasty pudding, hominy grits, hot cereal, kasha,
   loblolly, millet, mush, porridge, puffed rice, puffed wheat,
   rolled oats, wheatflakes