non compos mentis

Meanings

1. 1
   adj

   not of sound mind; unable to understand or take legal responsibility for one's actions

   The court had to decide whether he had been non compos mentis when he signed the document.

Borrowed unchanged from Latin non compos mentis, literally "not master of one's mind": non ("not") + compos ("having control") + mentis, the genitive of mens ("mind"). English legal use is recorded from the early seventeenth century; non compos is an informal shortening.

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