/ ˌɪdiəˈmætɪk; NAmE / adjective
1.
containing expressions that are natural to a native speaker of a language :
She speaks fluent and idiomatic English.
2.
containing an idiom :
an idiomatic expression
► idiom·at·ic·al·ly / -kli; NAmE / adverb
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WORD ORIGIN
early 18th cent.: from Greek idiōmatikos peculiar, characteristic, from idiōma private property, peculiar phraseology, from idiousthai make one's own, from idios own, private.