de·fea·sance /di-'fē-zəns/ n [Anglo-French defesance, literally, undoing, destruction, from Old French deffesant, present participle of deffaire to destroy, undo see defeat]
1 a: a condition (as in a deed or will) that upon fulfillment terminates a property interest
b: an instrument setting forth such a condition
2: a rendering null or void
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.