idiom vs parlance

idiom and parlance both are nouns.

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

As nouns, idiom and parlance are synonyms defined as:

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

idiom (noun)	parlance (noun)
the style of a particular artist or school or movement	a manner of speaking that is natural to native speakers of a language
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