idiom vs dialect

idiom and dialect both are nouns.

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

As nouns, idiom and dialect are synonyms defined as:

idiom and dialect: the usage or vocabulary that is characteristic of a specific group of people

Other synonyms of idiom include accent.

idiom (noun)	dialect (noun)
the style of a particular artist or school or movement	the usage or vocabulary that is characteristic of a specific group of people
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