idiom vs idiomatical

idiom is a noun but idiomatical is not a noun.

Word	Noun	Adjective	Verb	Adverb
idiom	Yes	No	No	No
idiomatical	No	Yes	No	No

idiom (noun)	idiomatical (noun)
the style of a particular artist or school or movement
the usage or vocabulary that is characteristic of a specific group of people
an expression whose meanings cannot be inferred from the meanings of the words that make it up
a manner of speaking that is natural to native speakers of a language

idiom (adjective)	idiomatical (adjective)
	of or relating to or conforming to idiom