Source : Webster's Revised Unabridged Dictionary (1913)

Sustainment \Sus*tain"ment\, n.
   The act of sustaining; maintenance; support. --Milton.
   Lowell.

Source : WordNet®

sustainment
     n : 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},
          {maintenance}, {upkeep}]