The Collaborative International Dictionary of English v.0.48:

Sustentation \Sus`ten*ta"tion\, n. [L. sustentatio sustenance,
   maintenance, fr. sustentare to support, maintain, v. intens.
   fr. sustinere to sustain: cf. F. sustentation. See
   Sustain.]
   1. The act of sustaining, or the state of being sustained;
      preservation from falling; support; sustenance;
      maintenance.
      [1913 Webster]

   2. (Physiol.) The aggregate of the functions by which a
      living organism is maintained in a normal condition of
      weight and growth.
      [1913 Webster]

   Sustentation fund (Eccl.), a fund of a religious body for
      support of its ministers, chapels, etc.; as, the
      sustentation fund of the Free Church of Scotland.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sustentation
    n 1: the act of sustaining life by food or providing a means of
         subsistence; "they were in want of sustenance"; "fishing
         was their main sustainment" [syn: sustenance,
         sustentation, sustainment, maintenance, upkeep]