mode vs idiom

mode and idiom both are nouns.

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

As nouns, idiom is a hyponym of mode; that is, idiom is a word with a more specific, narrower meaning than mode:

mode (noun)	idiom (noun)
how something is done or how it happens	the style of a particular artist or school or movement
the most frequent value of a random variable	the usage or vocabulary that is characteristic of a specific group of people
any of various fixed orders of the various diatonic notes within an octave	an expression whose meanings cannot be inferred from the meanings of the words that make it up
a classification of propositions on the basis of whether they claim necessity or possibility or impossibility	a manner of speaking that is natural to native speakers of a language
verb inflections that express how the action or state is conceived by the speaker
a particular functioning condition or arrangement