Ill-formed and Ill-defined

Ill-formed adjective - Not grammatical; not conforming to the rules of grammar or accepted usage.

Ill-defined and ill-formed are semantically related. In some cases you can use "Ill-defined" instead an adjective phrase "Ill-formed".

Ill-defined adjective - Poorly stated or described.

Ill-formed and ill-defined are semantically related. Sometimes you can use "Ill-formed" instead an adjective phrase "Ill-defined".