not enforceable; not capable of being brought about by compulsion; "an unenforceable law"; "unenforceable reforms"

The inability to enforce a contract in a court of law, including a promissory note, because of deficiencies in the contract or in the process used to create the contract.

Oral or written contract that is not enforceable by the judicial system.

A contract that is valid on it's face, but it's enforcement would violate the law.

An unenforceable contract or transaction is one that is valid, but which the court will not enforce. Unenforceable is usually used in contradistinction to void (or void ab initio) and voidable. If the parties perform the agreement, it will be valid, but the court will not compel them if they do not.