plea of insanity vs insanity plea

plea of insanity and insanity plea both are nouns.

Word	Noun	Adjective	Verb	Adverb
plea of insanity	Yes	No	No	No
insanity plea	Yes	No	No	No

As nouns, plea of insanity and insanity plea are synonyms defined as:

plea of insanity and insanity plea: (criminal law) a plea in which the defendant claims innocence due to mental incompetence at the time

plea of insanity (noun)	insanity plea (noun)
(criminal law) a plea in which the defendant claims innocence due to mental incompetence at the time	(criminal law) a plea in which the defendant claims innocence due to mental incompetence at the time