NOUN (3)

1. the process of decomposing organic matter (as in sewage) by bacteria or by chemical action or heat;

2. the organic process by which food is converted into substances that can be absorbed into the body;

3. learning and coming to understand ideas and information;
- Example: "his appetite for facts was better than his digestion"

The Collaborative International Dictionary of English v.0.48:

Digestion \Di*ges"tion\ (?; 106), n. [F. digestion, L.
   digestio.]
   1. The act or process of digesting; reduction to order;
      classification; thoughtful consideration.
      [1913 Webster]

   2. (Physiol.) The conversion of food, in the stomach and
      intestines, into soluble and diffusible products, capable
      of being absorbed by the blood.
      [1913 Webster]

   3. (Med.) Generation of pus; suppuration.
      [1913 Webster]

WordNet (r) 3.0 (2006):

digestion
    n 1: the process of decomposing organic matter (as in sewage) by
         bacteria or by chemical action or heat
    2: the organic process by which food is converted into
       substances that can be absorbed into the body
    3: learning and coming to understand ideas and information; "his
       appetite for facts was better than his digestion"

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "digestion":
   ablation, absorbency, absorbent, absorption, adsorbent, adsorption,
   assimilation, attrition, bile, blending, blotter, blotting,
   blotting paper, burning up, chemisorption, chemosorption,
   consumption, depletion, digestive system, drain, eating up,
   endosmosis, engrossment, erosion, exhaustion, exosmosis, expending,
   expenditure, finishing, gastric juice, gastrointestinal tract,
   imbibing, impoverishment, infiltration, ingestion,
   intestinal juice, liver, maceration, mastication, osmosis,
   pancreas, pancreatic digestion, pancreatic juice, percolation,
   predigestion, pulpefaction, pulpification, pulping, saliva,
   salivary digestion, salivary glands, secondary digestion, seepage,
   soaking-up, sorption, spending, sponge, sponging, squandering,
   taking-in, using up, wastage, waste, wastefulness, wasting away,
   wearing away, wearing down



The Devil's Dictionary (1881-1906):

DIGESTION, n.  The conversion of victuals into virtues.  When the
process is imperfect, vices are evolved instead -- a circumstance from
which that wicked writer, Dr. Jeremiah Blenn, infers that the ladies
are the greater sufferers from dyspepsia.