DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   defeasible
       adj 1: 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]