NOUN (3)

1. minimal (or marginal) resources for subsisting;
- Example: "social security provided only a bare subsistence"

2. a means of surviving;
- Example: "farming is a hard means of subsistence"

3. the state of existing in reality; having substance;

The Collaborative International Dictionary of English v.0.48:

Subsistence \Sub*sist"ence\, n. [Cf. F. subsistance, L.
   subsistentia.]
   1. Real being; existence.
      [1913 Webster]

            Not only the things had subsistence, but the very
            images were of some creatures existing.
                                                  --Stillingfleet.
      [1913 Webster]

   2. Inherency; as, the subsistence of qualities in bodies.
      [1913 Webster]

   3. That which furnishes support to animal life; means of
      support; provisions, or that which produces provisions;
      livelihood; as, a meager subsistence.
      [1913 Webster]

            His viceroy could only propose to himself a
            comfortable subsistence out of the plunder of his
            province.                             --Addison.
      [1913 Webster]

   4. (Theol.) Same as Hypostasis, 2. --Hooker.
      [1913 Webster]

WordNet (r) 3.0 (2006):

subsistence
    n 1: minimal (or marginal) resources for subsisting; "social
         security provided only a bare subsistence"
    2: a means of surviving; "farming is a hard means of
       subsistence"
    3: the state of existing in reality; having substance

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "subsistence":
   Lenten, Spartan, TLC, abstemious, accommodation, accommodations,
   aliment, alimentation, alimony, ascetic, austere, bed,
   bed and board, being, board, board and room, bread,
   bread and butter, care, daily bread, dwarfed, dwarfish,
   economic support, endowment, ens, entity, esse, essence, exiguous,
   existence, facilities, food, frugal, impoverished, jejune, keep,
   lean, life, limited, livelihood, living, lodgings, maintenance,
   manna, materiality, meager, mean, meat, miserly, mothering, narrow,
   niggardly, nourishment, nurture, nutriment, occurrence, paltry,
   parsimonious, poor, presence, price support, provision, puny,
   rations, salt, scant, scanty, scrawny, scrimp, scrimpy, skimp,
   skimpy, slender, slight, slim, small, spare, sparing, starvation,
   stingy, stinted, straitened, stunted, subsidization, subsidy,
   subsisting, substantiality, subvention, support, survival,
   sustainment, sustenance, sustentation, tender loving care, thin,
   unnourishing, unnutritious, upkeep, victuals, watered, watery