defeasible

Capable of being annulled or invalidated: a defeasible claim to an estate.

Capable of being overturned by further events. At law a judgement is defeasible if a higher court may overturn it. A proposition is defeasible if further evidence may render it doubtful.

Potentially subject to defeat, termination, or annulment upon the occurrence of a future action or event, or the performance of a condition subsequent.

The most common legal application of the term is with respect to estates as interest in land, such as in the case of a conveyance or a life estate, which is defeasible upon the happening of a certain specified event, for example, the death of the person holding such an interest.

The adjective has one meaning:

Meaning #1: capable of being annulled or voided or terminated
  Antonym: indefeasible (meaning #1)