The Collaborative International Dictionary of English v.0.48:
Compos mentis \Com"pos men"tis\ a. [L.] (Law) Sane in mind; being of sound mind, memory, and understanding. [Webster 1913 Suppl.]WordNet (r) 3.0 (2006):
compos mentis adj 1: of sound mind, memory, and understanding; in law, competent to go to trial [syn: compos mentis(p), of sound mind(p)]Bouvier's Law Dictionary, Revised 6th Ed (1856):
COMPOS MENTIS. Of sound mind. See non compos mentis.