Source : Webster's Revised Unabridged Dictionary (1913)

Compos mentis \Com"pos men"tis\ [L.] (Law)
   Sane in mind; being of sound mind, memory, and understanding.

Source : WordNet®

compos mentis
     adj : of sound mind, memory, and understanding; in law, competent
           to got to trial [syn: {compos mentis(p)}, {of sound
           mind(p)}]