google definitions - "define: insanity"
wordnet.princeton.edu/perl/webwn - relatively permanent disorder of the mind
en.wikipedia.org/wiki/Insanity - Insanity (sometimes, madness) is a semi-permanent severe disorder of the mind, typically as a result of mental illness.
and more interestingly:
www.psychologyandlaw.com/Definitions.htm - strictly a legal term, not a clinical term, the definition of which varies by jurisdiction. In most jurisdictions, this legal concept means a severe mental illness extant at the time the crime was committed such that the illness substantially impaired the defendant's capacity to understand and appreciate the moral wrongfulness of the act. A small minority of jurisdictions differentiate moral and legal wrongfulness. ...