Ill-formed and Unformed

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

Unformed and ill-formed are semantically related. in shapely topic. In some cases you can use "Unformed" instead an adjective phrase "Ill-formed", when it comes to topics like formless, shapeless.

Unformed adjective - Having no definite or recognizable form.

Ill-formed and unformed are semantically related. Sometimes you can use "Ill-formed" instead an adjective "Unformed".