The Collaborative International Dictionary of English v.0.48:

Rumination \Ru`mi*na"tion\, n. [L. ruminatio: cf. F.
   rumination.]
   1. The act or process of ruminating, or chewing the cud; the
      habit of chewing the cud.
      [1913 Webster]

            Rumination is given to animals to enable them at
            once to lay up a great store of food, and afterward
            to chew it.                           --Arbuthnot.
      [1913 Webster]

   2. The state of being disposed to ruminate or ponder;
      deliberate meditation or reflection.
      [1913 Webster]

            Retiring full of rumination sad.      --Thomson.
      [1913 Webster]

   3. (Physiol.) The regurgitation of food from the stomach
      after it has been swallowed, -- occasionally observed as a
      morbid phenomenon in man.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rumination
    n 1: a calm, lengthy, intent consideration [syn:
         contemplation, reflection, reflexion, rumination,
         musing, thoughtfulness]
    2: (of ruminants) chewing (the cud); "ruminants have remarkable
       powers of rumination"
    3: regurgitation of small amounts of food; seen in some infants
       after feeding