defeasance

noun Law.

1. a rendering null and void.
2. a condition on the performance of which a deed or other instrument is defeated or rendered void.
3. a collateral deed or other writing embodying such a condition.

noun mainly law

1. the act or process of rendering null and void; annulment
2. 1. a condition, the fulfilment of which renders a deed void
   2. the document containing such a condition

n.

early 15c., from Anglo-French defesaunce, Old French desfaisance “undoing, destruction,” from desfaire (Modern French défaire) “to undo, destroy” (see defeat (v.)). Related: Defease; defeasible.