The antonyms for the word "un-treated" are "treated", "processed", "cured", "healed", and "remediated". These words represent the opposite of "un-treated", indicating that the subject in question has undergone some form of treatment or processing. For instance, treated lumber is lumber that has undergone some form of processing or treatment to make it resistant to insects and rot. Similarly, a cured patient has undergone treatment for their illness and is now healthy. Healed skin has undergone treatment to restore it to its natural state, and remediated land has undergone some form of treatment to clean up any pollutants. Therefore, antonyms for "un-treated" signify a process that has been applied to treat, cure or improve a subject.