The Collaborative International Dictionary of English v.0.48:

Nutrition \Nu*tri"tion\, n. [Cf. F. nutrition. See
   Nutritious.]
   1. (Physiol.) In the broadest sense, a process or series of
      processes by which a living organism as a whole (or its
      component parts or organs) is maintained in its normal
      condition of life and growth.
      [1913 Webster]

   Note: In this wide sense it comprehends digestion,
         absorption, circulation, assimilation, etc., in fact
         all of the steps by which the nutritive matter of the
         food is fitted for incorporation with the different
         tissues, and the changes which it undergoes after its
         assimilation, prior to its excretion. See Metabolism.
         [1913 Webster]

   2. (Physiol.) In a more limited sense, the process by which
      the living tissues take up, from the blood, matters
      necessary either for their repair or for the performance
      of their healthy functions.
      [1913 Webster]

   3. That which nourishes; nutriment.
      [1913 Webster]

            Fixed like a plant, on his peculiar spot,
            To draw nutrition, propagate, and rot. --Pope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nutrition
    n 1: (physiology) the organic process of nourishing or being
         nourished; the processes by which an organism assimilates
         food and uses it for growth and maintenance
    2: a source of materials to nourish the body [syn: nutriment,
       nourishment, nutrition, sustenance, aliment,
       alimentation, victuals]
    3: the scientific study of food and drink (especially in humans)

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "nutrition":
   appetite, baking, barbecuing, basting, boiling, braising, brewing,
   broil, broiling, cannibalism, carnivorism, carnivority,
   carnivorousness, catering, chewing, consumption, cookery, cooking,
   cropping, cuisine, culinary science, deglutition, devouring,
   devourment, dieting, dining, domestic science, eating, epulation,
   feasting, feeding, frying, gluttony, gobbling, grazing, grilling,
   herbivorism, herbivority, herbivorousness, home economics, hunger,
   ingestion, licking, manducation, mastication, messing, munching,
   nibbling, omnivorism, omnivorousness, omophagy, pan-broiling,
   pantophagy, pasture, pasturing, pecking, poaching, regalement,
   relishing, roasting, rumination, sauteing, savoring, searing,
   shirring, simmering, steeping, stewing, tasting, toasting,
   vegetarianism, wolfing