The Collaborative International Dictionary of English v.0.48:

Inveteracy \In*vet"er*a*cy\, n. [From Inveterate.]
   [1913 Webster]
   1. Firm establishment by long continuance; firmness or
      deep-rooted obstinacy of any quality or state acquired by
      time; as, the inveteracy of custom, habit, or disease; --
      usually in a bad sense; as, the inveteracy of prejudice or
      of error.
      [1913 Webster]

            An inveteracy of evil habits that will prompt him to
            contract more.                        --A. Tucker.
      [1913 Webster]

   2. Malignity; spitefulness; virulency.
      [1913 Webster]

            The rancor of pamphlets, the inveteracy of epigrams,
            and the mortification of lampoons.    --Guardian.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "inveteracy":
   abidingness, aboriginality, accustomedness, age, ancien regime,
   ancientness, antiquity, atavism, changelessness,
   cobwebs of antiquity, commonness, confirmation, confirmedness,
   constancy, customariness, deep-rootedness, deep-seatedness,
   durability, durableness, duration, dust of ages, eld, elderliness,
   eldership, embedment, endurance, entrenchment, establishment,
   firmness, fixation, fixedness, fixity, fixture, frozenness,
   great age, habitualness, hardening, hoary age, hoary eld,
   immobility, immovability, immovableness, immutability,
   implantation, infixion, invariability, invariableness,
   inveterateness, lastingness, long standing, old age, old order,
   old style, oldness, permanence, permanency, perpetualness,
   persistence, persistency, prevalence, primitiveness, primogeniture,
   primordialism, primordiality, quiescence, rigidity, senility,
   seniority, settledness, solidity, stability, stabilization,
   standing, stasis, steadfastness, torpor, unchangeability,
   unchangingness, venerableness, wontedness