Source : Webster's Revised Unabridged Dictionary (1913)

Appurtenance \Ap*pur"te*nance\, n. [OF. apurtenaunce,
   apartenance, F. appartenance, LL. appartenentia, from L.
   appertinere. See {Appertain}.]
   That which belongs to something else; an adjunct; an
   appendage; an accessory; something annexed to another thing
   more worthy; in common parlance and legal acceptation,
   something belonging to another thing as principal, and which
   passes as incident to it, as a right of way, or other
   easement to land; a right of common to pasture, an outhouse,
   barn, garden, or orchard, to a house or messuage. In a strict
   legal sense, land can never pass as an appurtenance to land.
   --Tomlins. --Bouvier. --Burrill.

         Globes . . . provided as appurtenances to astronomy.
                                                  --Bacon.

         The structure of the eye, and of its appurtenances.
                                                  --Reid.

Source : WordNet®

appurtenance
     n : a supplementary component that improves capability [syn: {accessory},
          {supplement}, {add-on}]