The term "unsound mind" refers to someone who is mentally unstable or insane. There are several synonyms for this term, including deranged, unhinged, crazy, insane, mentally ill, lunatic, psychotic, and demented, among others. Some of these terms have different nuances to their meaning. For instance, "deranged" suggests a state of extreme madness, while "unhinged" refers to someone who has lost touch with reality. The word "crazy" is more colloquial and can be used to describe any type of unpredictable or illogical behavior. "Insane" and "mentally ill" are more clinical terms used to describe a range of disorders. Overall, these synonyms express the idea of someone who is not mentally well.