The Collaborative International Dictionary of English v.0.48:

Revertible \Re*vert"i*ble\, a.
   Capable of, or admitting of, reverting or being reverted; as,
   a revertible estate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

revertible
    adj 1: to be returned to the former owner or that owner's heirs

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "revertible":
   atavistic, compensatory, indemnificatory, reactionary, recessive,
   recidivist, recidivous, redeeming, redemptional, redemptive,
   regressive, reparative, restitutive, restitutory, restorative,
   retributive, retrograde, retrogressive, retrorse, retroverse,
   returnable, reversible, reversional, reversionary, revulsionary