Source : Webster's Revised Unabridged Dictionary (1913)

Defeasible \De*fea"si*ble\, a. [See {Defeasance}.]
   Capable of being annulled or made void; as, a defeasible
   title. -- {De*fea"si*ble*ness}, n.

Source : WordNet®

defeasible
     adj : capable of being annulled or voided or terminated; "a claim
           to an estate may be defeasible so long as the claimant
           is under 21 and unmarried" [ant: {indefeasible}]