The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Globes . . . provided as appurtenances to astronomy.
                                                  --Bacon.
   [1913 Webster]

         The structure of the eye, and of its appurtenances.
                                                  --Reid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

appurtenance
    n 1: equipment consisting of miscellaneous articles needed for a
         particular operation or sport etc. [syn: gear,
         paraphernalia, appurtenance]
    2: a supplementary component that improves capability [syn:
       accessory, appurtenance, supplement, add-on]