insanity plea
Noun
Meaning
(criminal law) a plea in which the defendant claims innocence due to mental incompetence at the time
Source: WordNetSynonyms
Hypernyms
Examples
Is not this insanity plea becoming rather common? Is it not so common that the reader confidently expects to see it offered in every criminal case that comes before the courts? [...] Really, what we want now, is not laws against crime, but a law against insanity.
We have an insanity plea that would have saved Cain.