The Collaborative International Dictionary of English v.0.48:

Casserole \Cas"se*role\n. [F. a saucepan, dim. from casse a
   basin.]
   1. (Chem.) A small round dish with a handle, usually of
      porcelain.
      [1913 Webster]

   2. (Cookery) A mold (in the shape of a hollow vessel or
      incasement) of boiled rice, mashed potato or paste, baked,
      and afterwards filled with vegetables or meat.
      [1913 Webster]

WordNet (r) 3.0 (2006):

casserole
    n 1: food cooked and served in a casserole
    2: large deep dish in which food can be cooked and served