The Collaborative International Dictionary of English v.0.48:

Non compos \Non com"pos\ Non compos mentis \Non com"pos men"tis\
   [L.]
   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.
   [1913 Webster]