The Collaborative International Dictionary
Non compos \Non com"pos\ Non compos mentis \Non com"pos men"tis\ Not of sound mind; not having the regular use of reason; hence, also, as a noun, an idiot; a lunatic; one devoid of reason, either by nature or from accident.
Wiktionary
a. (alternative form of non compos mentis English)
Usage examples of "non compos".
How can you do or say anything calling for an apology when you are legally non compos mentis?
Hughes is non compos mental, and he thinks he's got Ward in his pocket.
The fact that he is clearly non compos mentis will carry no weight with the Prince when he gets wind of this.
But the old Latin joke came back to him: Penis erectus non compos mentis.
I went to Felix's parties and I trucked with Georgie once, and Felix thought I was non compos mentis, so if he sent you to see me he was probably playing a game.