parlance vs idiom

parlance and idiom both are nouns.

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

As nouns, parlance and idiom are synonyms defined as:

parlance and idiom: a manner of speaking that is natural to native speakers of a language

parlance (noun)	idiom (noun)
a manner of speaking that is natural to native speakers of a language	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